Use of the passive voice	

The Harry Potter stories are a series of popular fantasy adventure stories. J K Rowling wrote them between 1997 and 2997.	The Harry Potter stories are a series of popular fantasy adventure stories. They were written by J K Rowling between 1997 and 2997.	The Harry Potter stories are a series of popular fantasy adventure stories. They were written between 1997 and 2997.	
Workers are demolishing that building.	That building is being demolished by workers.	That building is being demolished.	
They make shampoo in that factory.	Shampoo is made in that factory.	Workers make shampoo in that factory.	
Scientists discovered anaesthetics in the 19th century	Anaesthetics were discovered in the 19th century.	Anaesthetics were discovered by scientists in the 19th century.	
Cars parked here will be towed away.	Cars parked here will be towed away by our staff.	We will tow your car away if you park it here.	
The new model has been a resounding success. Our sales staff sold over 30,000 units in March.	The new model has been a resounding success. Over 30,000 units were sold in March.	The new model has been a resounding success. Over 30,000 units were sold by our sales staff in March.	
They’ve repainted the building.	The building has been repainted by them.	The building has been repainted.	
Chek Lap Kok Airport opened in 1998. Sir Norman Foster designed it
and the workers took seven years to build it.	Chek Lap Kok Airport was opened by the HK Airport Authority in 1998. It was designed by Sir Norman Foster and took seven years to build by the workers.	Chek Lap Kok Airport was opened in 1998. It was designed by Sir Norman Foster and took seven years to build.	
Bills must be paid in full by customers on the day of treatment.	Bills must be paid in full on the day of treatment.	You must pay your bill in full on the day of treatment.	
We will disconnect your electricity supply if you do not settle the bill by 12 August.	Your electricity supply will be disconnected by us if the bill is not settled by you by 12 August.	Your electricity supply will be disconnected if the bill is not settled by 12 August.	
The new bridge across the harbour was competed in July 2012 and was opened on August 1.	The new bridge across the harbour was competed in July 2012 and was opened by the President on August 1.	The new bridge across the harbour was competed in July 2012 and the President opened it on August 1	

Answers

The Harry Potter stories are a series of popular fantasy adventure stories. J K Rowling wrote them between 1997 and 2997.	The Harry Potter stories are a series of popular fantasy adventure stories. They were written by J K Rowling between 1997 and 2997.	The Harry Potter stories are a series of popular fantasy adventure stories. They were written between 1997 and 2997.	
Workers are demolishing that building.	That building is being demolished by workers.	That building is being demolished.	
They make shampoo in that factory.	Shampoo is made in that factory.	Workers make shampoo in that factory.	
Scientists discovered anaesthetics in the 19th century	Anaesthetics were discovered in the 19th century.	Anaesthetics were discovered by scientists in the 19th century.	
Cars parked here will be towed away.	Cars parked here will be towed away by our staff.	We will tow your car away if you park it here.	
The new model has been a resounding success. Our sales staff sold over 30,000 units in March.	The new model has been a resounding success. Over 30,000 units were sold in March.	The new model has been a resounding success. Over 30,000 units were sold by our sales staff in March.	
They’ve repainted the building.	The building has been repainted by them.	The building has been repainted.	
Chek Lap Kok Airport opened in 1998. Sir Norman Foster designed it
and the workers took seven years to build it.	Chek Lap Kok Airport was opened by the HK Airport Authority in 1998. It was designed by Sir Norman Foster and took seven years to build by the workers.	Chek Lap Kok Airport was opened in 1998. It was designed by Sir Norman Foster and took seven years to build.	
Bills must be paid in full by customers on the day of treatment.	Bills must be paid in full on the day of treatment.	You must pay your bill in full on the day of treatment.	
We will disconnect your electricity supply if you do not settle the bill by 12 August.	Your electricity supply will be disconnected by us if the bill is not settled by you by 12 August.	Your electricity supply will be disconnected if the bill is not settled by 12 August.	
The new bridge across the harbour was competed in July 2012 and was opened on August 1.	The new bridge across the harbour was competed in July 2012 and was opened by the President on August 1.	The new bridge across the harbour was competed in July 2012 and the President opened it on August 1