Puzzling questions

Find the mistake in these sentences:

1. I don't know why she is upset, but she must have had bad news.

2. I may have lost my keys. I'm sure they were in my pockets.

My answers

1. I don't know why she is upset, but she may have had bad news.

2. I must have lost my keys. I'm sure they were in my pockets.

((What do you think of my answers?))



Choose the correct answer:

1. She......rung me this morning. I was out until midday.

a) must have b) could have

((I think both choices are ok.))