have to or had to

[hoangkha]

Hi, teacher!
I have seen this sentence.
They wanted to know why they _____________ it for her while she could do it by herself.

A. did
B. should do
C. have done
D. have to do
The key is D, but I think it should be HAD TO instead of HAVE TO. Is it right, please?

[bhaisahab]

Hi, teacher!
I have seen this sentence.
They wanted to know why they _____________ it for her while she could do it by herself.

A. did
B. should do
C. have done
D. have to do
The key is D, but I think it should be HAD TO instead of HAVE TO. Is it right, please?

Yes, it should be "had to". I would change "while" to "when", too.