he teacher told them since light ________ (travel) faster than sound,lightning ________ (appear) to go before thunder.

________(fail)severaltimes,theyneedsomeencouragement.

Iknowitisn’timportantbutIcan’thelp________aboutit.

A beam of light will not bend round corners unless ________ (make) to do so with the help of a reflecting device

I wonder if he could get it ________ (do) before tomorrow.