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：(C) encouraging
現在分詞片語 encouraging，補充說明前面主要子句的結果／伴隨動作，表示「（笑）促進白血球的產生」；句子已經有主要動詞 has，不需要再用限定動詞 encourages；encouraged（過去分詞，被動，語意方向相反，應該是笑「促進」而非笑「被促進」）、to encourage（不定詞，不符合這個分詞構句結構）都不合。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
四個選項是 encourage 的四種形態，你會開始判斷這一串是分詞構句還是限定動詞、意義主詞是誰、要主動還是被動。其實不必想那麼遠——答案就寫在同一句話的後半段。
四個選項都是同一個動詞 encourage 的形態，可見這一格考的是形態。先把整句拉出來：Laughter, too, has a beneficial effect on our immune system, ___ the production of white blood cells and increasing our resistance to infection.注意逗號後面那一串的結尾：and increasing our resistance to infection——and 後面是 increasing，一個現在分詞。and 兩邊要對等，既然後面那一個是現在分詞，空格就照抄現在分詞，填 encouraging。這就是並列結構「照抄另一邊的形態」那一招（同型：88 年第 23 題、95 年第 27 題、99 年第 27 題、100 年第 19 題）。用了這一招，就完全不必去判斷分詞的主動被動——答案在 and 的另一邊。如果要驗算也很簡單：整句已經有主要動詞 has 了，逗號後面那兩串是補充說明笑所帶來的結果，還原成 and it encourages the production ... and increases our resistance ...。
encourages：限定動詞。句子已經有主要動詞 has，再放一個限定動詞而中間只用逗號連接，會變成兩個句子黏在一起。encouraged：過去分詞表被動，方向錯了——是笑促進白血球的產生，不是笑被促進。to encourage：不定詞表目的，但這兩串講的是笑造成的結果，不是笑的目的；而且與 and 後面的 increasing 對不齊。
have a beneficial effect on（對……有益）、encourage the production of（促進……的產生）、resistance to infection（對感染的抵抗力）、the immune system（免疫系統）、white blood cells（白血球）、increase（增加、提高）。
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.