It __be the vocabulary that caused you the problem in the exercise because you know a lot of words.

—Whose workbook is this, Tony?—Look! Ann's name is on it! It ______ be hers.

---I think _________________ in the morning is a good way to improve your spoken English. ---I agree with you.

The driver ____ have drunk a lot before the accident, but I'm not quite sure of that．

I am feeling sick now．I ________ so much chocolate．