On foggy days, you have to drive very ________ on the expressway to avoid traffic accidents.

I could hardly tell the twins apart because their appearances are only ____ different.

Mary is very clever and_____ worth teaching , but her brother is not .Look he is now _____ asleep in class.

I don’t mind picking up your things from the store. ______, the walk will do me good.

Bicycling is good exercise; ____, it does not pollute the air.