He started to learn English in 1990 and in the years ________ he kept on using it in his work.
You can find whatever you need at the shopping centre,_____is always busy at the weekend.
These newly-produced cars are sold at so low a price_____people expected.
The most important thing_____we should pay attention to is the first thing _____I have said.
The World Wide Fund for Nature is an organization_____aim is to protect wildlife.
A container weighs more after air is put in,_____proves that air has weight.