Unless she doesn’t know who it is, she won’t open the door

Unless she doesn’t know who it is, she won’t open the door *
A. won’t open
B. who
C. it is
D. doesn’t know
Mark went on working despite he felt unwell *
A. went on
B. working
C. despite
D. felt
The waiter whom served us yesterday was polite and friendly. *
A. was
B. friendly
C. whom
D. The