Although she had been known as an effective legislator first

This sentence has modifier and agreement issue.

The sentence starts with description of “Barbara Jordan” role. So we require “Barbara Jordan” - Eliminate A, C and D

Between B and E: “Which” logically modifies “hearings” so require plural verb – So B wins

Also In E: "then also later" is verbose

B for me too.

P.S. Question seems to have unnecessary words underlined.

friends, can someone tell me what´s wrong with C?

Although she had been known as an effective legislator first in the Texas Senate and later in the United States House of Representatives, not until Barbara Jordan’s participation in the hearings on the impeachment of President Richard Nixon in 1974 was she made a nationally recognized figure, as it was televised nationwide.

A. later in the United States House of Representatives, not until Barbara Jordan’sparticipation in the hearings on the impeachment of President Richard Nixon in
1974 was she made a nationally recognized figure, as it was

B. later in the United States House of Representatives, Barbara Jordan did not
become a nationally recognized figure until 1974, when she participated in the
hearings on the impeachment of President Richard Nixon, which were

C. later in the Untied States House of Representatives, it was not until 1974 that
Barbara Jordan became a nationally recognized figure, with her participation in
the hearings on the impeachment of President Richard Nixon, which was

D. then also later in the United States House of Representatives, not until 1974 did
Barbara Jordan become a nationally recognized figure, as she participated in the
hearings on the impeachment of President Richard Nixon, being

E. then also later in the United States House of Representatives, Barbara Jordan did
not become a nationally recognized figure until 1974, when she participated in the
hearings on the impeachment of President Richard Nixon, which was

this SC is pretty long i got confused between two options !!help me out !is there any strategy to deal with long SCs

Which refers to the word right before comma and in both B & E, it seems to refer to Richard Nixon.

What is the source of this Q?

Yes same issue i faced !!! which appears to point to richard nixon.But hearings can be televised hence B is true .now im clear on this !!

question is from some doc i had.

It does not matter whether hearings can be televised or not. Which always refers to the thing right before the comma.