D. The social context of the 1960's discouraged innovation and exploration because people were afraid of new technologies and feared being overrun by space aliens.
The answer is B: Less than a decade ago, the HSUS...an affiliate [Human Society International].
Brackets are used to give the writers (when they need to add information) an opportunity to add an explanation, or emphasis to a word, or change a <em>quote to fit to a sentence, but without changing the meaning of the text</em>. In A) <em>global work</em> doesn't need explanation; C) <em>decade</em> doesn't need explanation; D) <em>HSUS</em> was already explained in the first sentence of the text.
The best answer is B, because if the school has only women gym teacher then you can't have a male gym teacher.
