Student or Learner
Why is b the only answer? I think c can be, too. When you use "a" it's one of many, unspecific, so if there's many other kinds of documentaries except this, it's possible, but if there's only of this documentary, then this should be "the". I don't understand why b is the only answer, the tester may have made a mistake.
Q. The TV studio on the third floor is renowned for ___b____ of producing award-winning documentaries.
b)an extensive history
c)the extensive history
d)any extensive history
It's the history that's extensive, not the documentaries.
However, I don't like any of those choices. I'd say "its" instead of "an."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.