modals or ... (Although he seems to be studying hard for the exam, I'm quite...)

[Penuel]

Hello!
Please help me to choose the correct answer for:
Although he seems to be studying hard for the exam, I'm quite doubtful whether he..................
a) is going to pass
b) will pass
c) could pass
d) might passing
e) would pass

Thanks a million!

[Kitosdad]

Good morning Penuel, not so easy this one, but I would choose a), the whole sentence reeks of uncertainty.
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If you need me, I'm here.

[Penuel]

And here is another one:

Why ... the navigators ... to find new trade routes in the 15th century?
a) do ... tried
b) has ... tried
c) did tried
d) had ... tried

If any of these answers is correct please let me know why.

Thanks.

[Kitosdad]

I have already answered this on the other post.

d) is the correct form.

Kitosdad.
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