Please correct me if I am wrong

I really can't say whose ______ but I'll try to find out for you.
(A) is that computer
(B) computer is it
(C) computer that is
(D) computer
Answer (C)

If I ______ my physics class, I will graduate in May.
(A) will pass
(B) would pass
(C) passed
(D) pass
Answer (D)

Can you please mail this letter important
A B C
for me?
D
(A) Can you
(B) mail
(C) letter important
(D) for me
Answer (C)

Our stock is low. Do you think our assistant
A B
can order several new merchandise this week?
C D
(A) Do you
(B) assistant
(C) can order
(D) several
Answer (D)

My sister ______ go on vacation to Italy last month, but couldn't.
(A) will
(B) is going to
(C) should
(D) was going to
Answer (C)

Although my department always submits its annual report by the end of the year, some ______ wait until the end of January.
(A) had has to
(B) has had to
(C) have had to
(D) had to have
Answer (C)

As a result of heavy traffic, his flight left
A B C
by the time he got to the airport.
D
(A) As a result of
(B) heavy
(C) left
(D) got
Answer (D)

Man: Did you hear that when the Head of Finance offered Leslie a promotion, she refused?
Woman: Yes, if I were in her position, I ____________________ the job too.
(A) would have turned off
(B) will have turned down
(C) would have turned down
(D) will have turned away
Answer (C)