Laughter, too, has a beneficial effect on our immune system, 38 the production of white blood cells and increasing our resistance to infection.39 makes a difference to our appearance, too, when we relax our facial muscles!
答案：(A) It
虛主詞 It，代替後面「放鬆臉部肌肉」這件事整體，構成「It makes a difference...」的句型；There 用於 there be 句型不符合makes a difference的結構，What／Where 疑問詞都不能這樣單獨作主詞開頭。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
句尾有一個 when 子句，所以你可能會覺得空格要放一個疑問詞或連接詞，於是 What 或 Where 看起來有機會。但這一句是直述句不是問句，空格要的只是一個主詞。
先看空格後面接什麼：makes a difference to our appearance（讓我們的外表有所不同）。makes 是限定動詞，前面一定要有主詞，所以空格要填的是一個能當主詞的字。What 與 Where 是疑問詞，本句沒有問號、也不是間接問句，先出局。There 也不行：there 只用在 there is／there are／there seems to be 這一類存在句裡，不能當一般動詞 makes 的主詞（沒有 There makes ... 這種說法）。剩下 It——它指的是前面一直在講的 laughter（笑）。句尾的 too（也）正好印證：前一句說笑對免疫系統有益，這一句說笑「也」讓我們的外表不一樣。
There：存在句專用，接不了 makes。What、Where：疑問詞，本句是直述句。
make a difference to（對……有影響、使……不同）、It makes no difference.（沒差別）、relax one’s muscles（放鬆肌肉）、facial muscles（臉部肌肉）、appearance（外表）、too（也，置於句中或句尾）。
Perhaps most of us are familiar with the saying "Laugh and the world 31 with you, weep and you weep alone."32 did you know that according to recent research, people are losing the art of laughter and it could have a 33 effect on our health? In 1930 we laughed on average for 19 minutes each day, but by 1980 it 34 to six minutes. Children, 35 , can see the funny side of things more often and may laugh up to 400 times a day.
By exhaling air from the lungs in short 36 of laughter, breathing is quickened and heartbeats increased, which achieves 37 good as ten minutes on an exercise bike. Laughter, too, has a beneficial effect on our immune system, 38 the production of white blood cells and increasing our resistance to infection.39 makes a difference to our appearance, too, when we relax our facial muscles!
Laughter 40 is the best medicine, so why not give yourself a treat? Have a good laugh today--and feel better for it.