By now, when one makes a large purchase, he should have ___ opportunity to change his mind.

Although I am not good enough at my subjects, I want to be ______ university student in the future.

It was along the Mississippi River ________ Mark Twain spent much of his childhood.[ ]

I don’t care about the salary offered by the company. What I need is a (an) post.[ ]

The headmaster will __________ a speech tothe visiting foreign guests this afternoon.