Idiom error

A decade in THE MAKING,the documentary on penguins is BOTH A RESPONSE to widespread misinformation WITH their mating habits and AN INVESTIGATION into their behaviours. NO ERROR

This is a question from princeton… Ans is C
I marked D…
Please explain

It’s C because the answer is suppose to be “of their mating habits.”

In the explanantion,princeton says that with should be replaced with “about”

Either one could work, but C is definitely wrong. And also, this is not an idiom error, it is a preposition error.

Okay
Thanx

WHEN GORDON BAKED the pecan pie and served slices of it WITH VARIOUS toppings-including vanilla ice cream and sprinkles-he HAD BEEN the first TO EAT a slice.NO ERROR
guys pls tell me why “had been” is wrong… I really get confused with these type of questions…
Help will be appreciated…
Thanx in advance

A question from princeton

The verb should be in the simple past - WHEN GORDON BAKED the pecan pie and served slices of it WITH VARIOUS toppings-including vanilla ice cream and sprinkles-he WAS the first TO EAT a slice.

It needs to be in the same tense as the other past tense verbs (i.e., baked and served).

Okay thanx.