Grammar questions

1) The workers on both production teams should always communicate with ________.

(A)
another

(B)
the other

(C)
each

(D)
one another

I think it's D

2) He ________ in that company when he had the chance.


(A)
should invest

(B)
would have been invested

(C)
could be investing

(D)
should have invested

I think it's A or D. Please clarify. When he had the chance((as this is past perfect right)

3) A: Should people on sick leave be allowed to accumulate vacation time?
B: ______ federal regulations dictate our company leave policy.

(A)
Lacking options,

(B)
We are limited because

(C)
It's a moot point that

(D)
Due to the fact that

I think it's B. Please clarify with D, when we could use D the scenario in this situation?

4) We should have had the car to be repaired at the shop before trying to sell it. (Find the error)

(A)
should have

(B)
to be repaired

(C)
trying

(D)
to sell

I think it's B. Please confirm all answers