He is busy now, otherwise he ______ go with you for a walk.

The natural environment should be protected because of the important role _______ plays in human survival and development.

_____does it cost —Five hundred and fifty yuan.

Yesterday I went to buy a computer. There were so many models for us _____ in the shop that I was at a loss which to buy.

Is honesty the best policy? We _that it is when we are little