Ironically,the normally ....... speaker became shy and ..... when confronted with the approbatory stares of her eager audience.

The following sentence tells us that, "Ironically, the normally ....... speaker became shy"
That means the normal state we are looking for is on the opposite end of the spectrum of Shy. 

Let us look at the options: D is not relevant, A says quiet, which would be in line with shy, so this can be eliminated as well, and C as well is irrelevant. 

The answer is B. Garrulous means excessively talkative and reticent means not revealing one's thoughts easily. This is enough to say for certain that B is the answer.