SAT writing it's tomorrow! Please help me!

The heat was already overwhelming and lasted a week, which duration made it seem sheer torture.

a. overwhelming and lasted a week, which duration made it seem
b. overwhelming, and because of lasting a week, it made it seem
c. overwhelming and lasted the duration of a week to make it seem
d. overwhelming, and its lasting a week made it seem
e. overwhelming and, by lasting a week, making it seem

The answer is d. What does “its” implies to in choice d? If it is referring to heat, does it means heat’s? I don’t think that is right. Am I wrong?

Thanks in advance!

I think “its lasting” has to be read together. You would not write “the heat’s lasting a week made it seem …” and the fact that there is an independent clause at the start of the sentence doesn’t change anything.

The grammar experts are now free to chime in.

I forgot to put parenthesis…
The heat was already (overwhelming and lasted a week, which duration made it seem) sheer torture.

Thank you for replying!
Doesn’t “overwhelming, and its lasting a week made it seem” should be changed to “overwhelming, and it lasting a week made it seem”? Or are these both right? What difference does this make?

I think I got it now! Thank you!

Compare
I saw Mary playing at the tournament yesterday.
to
I saw Mary’s playing yesterday.
to
Mary was playing yesterday.

Present Participle and Gerund look identical (verb+ing); Present Continuous just adds “to be” in the right tense in front of the Present Participle,
They all serve different functions in the sentence.

More of Mary:
Bathing in the sun, Mary looks adorable.
Mary’s bathing in the sun is becoming obsessive.
Mary is bathing in the sun again.