His brother met him at the Great Theatre yesterday afternoon, so he ____ have attended your lecture. 

We        have bought so much food now that Suzie won’t be with us for dinner.

Swimming alone ___be ____dangerous. Do be careful.

—Why didn’t you put your cellphone in your overcoat pocket?—I ________, but I was afraid it would be stolen.

 I ______________ have passed my examination easily，but I made too many stupid mistakes．