이문제 해설좀 부탁드릴게요ㅠㅠ

* 다음 글을 읽고 물음에 답하시오.
when you are in danger and feel afraid, your body automatically produces a chemical, ①[calling/called] adrenalin, in your blood. with adrenalin in the blood system, you actually feel ②[strongly/stronger] and are ready to fight. ③[therefore/however], when you are absolutely terrified, your body can produce too ④[many/much] adrenalin. ⑤[since/when] this happens, your muscles become very ⑥[hardly/hard] and you find out ⑦[if/that] you can’t move at all. you are so frightenedthat you become like a stone.

답

① called
② stronger
③ however
④ much
⑤ when
⑥ hard
⑦ that