1) Sarah had always dreamed of becoming a newscaster, but her parents urged her to study accounting instead. If only she had been true to her vision, she __________ on TV by now.

a. should be

b. will possibly have been

c. could possibly have been

d. has possibly been

1) 답은 가정법 과거로 c인데 마지막 now 때문에 혼합 가정법으로 a가 가능하지 않나요?

2) The Clean Seas Optimists spokesperson, Amanda Watts, spoke about plastic being both a gift and a curse to humankind. It obviously benefits industries and consumers as packaging material _______ posing a threat to wildlife.

a. however

b. while

c. therefore

d. nevertheless

2) 답은 b인데 while은 접속사라서 뒤에 주어+동사가 필요한거 아닌가요?

3) Alpha Squad Leader Murphy Jones informed his men that they have to get past enemy lines before sundown. Sensing immediate danger ahead, he _________ his men on their best course of action.

a. is briefing

b. was briefing

c. had been briefing

d. has briefed

3) 답은 a인데 b - 과거시점이 안보여서 안되고 c,d가 안되는 이유 해설 부탁드립니다.