"might" or "must"

[jctgf]

Mike: She always goes to work on a bike.
Jane: .........

(a) She is very healthy.
(b) She must be very healthy.
(c) She can be very healthy.
(d) She might be very healthy.



Hi,
What's the answer, please?
I'd choose "B" but I still don't know very well when to use "must" and "might".
Thanks

[Soup]

(b) She must be very healthy.

"Must" is most commonly used to express certainty.

"Might" is most commonly used to express possibility.

Source: ENGLISH PAGE - Modal Verb Tutorial

[jctgf]

Soup,

Thanks a lot for your explanation. It really made a difference.
I took the test and for my surprise I only failed one question:

3. Nina said she would come over right after work, so she ______ be here by 6:00.

I answered "might" and the right one seems to be "should".
I don't see why it cannot be "might".
Is it because that's simply the way native speakers are used to say it?
What's your opinion, please?
Thanks.

[Soup]

3. Nina said she would come over right after work, so she ______ be here by 6:00.

You're most welcome.


She should / is expected to be here by 6:00.

"Should" is most commonly used to make recommendations or give advice. It can also be used to express obligation as well as expectation.

ENGLISH PAGE - Should