4. In an experiment pubished in 1988, social psychologist Fritz Strack of the University of Wurzburg in Germany asked volunteers to hold a pen either with their teeth—thereby creating an artificial smile—or with their lips, which would produce a disappointed expression.

【分析】復合句。句子主干為 social psychologist FritzStrack ...asked volunteers to hold a pen...。句首的介詞短語作整句話的狀語；either with ...or with... 作動詞 hold 的方式狀語，第一個狀語后的現在分詞短語作目的狀語，第二個狀語后 which 引導非限定性定語從句。

【譯文】1988年發表過一項實驗，德國維爾茨堡大學的社會心理學家弗里茨·斯特拉克和他的同事們招募了一批志愿者。他們讓一部分人用牙齒咬住一支筆，從而在臉上制造出“人工笑臉”；或是用嘴唇叼著筆，從而產生“沮喪表情”。

5. Those forced to exercise their smiling muscles reacted more enthusiastically to funny cartoons than did those whose mouths were contracted in a frown, suggesting that expressions may inflence emotions rather than just the other way around.

【分析】復合句。主句為 Those... reacted more enthusiastically to funny cartoons，過去分詞短語 forced to...作后置定語修飾 those。than 引導比較狀語從句，該從句中的主語 those 由定語從句修飾，因其較長，謂語又因與主句重復而省略為 did，所以用倒裝語序。suggeating... 為現在分詞結構作結果狀語，其中包含 that 引導的賓語從句。

【譯文】那些用牙齒咬著筆，表現出笑容的人比那些用嘴唇叼著筆、表現出沮喪神情的人在看搞笑的動畫片時所作出的反應更豐富。這就證明了表情能夠影響情緒，而不是情緒影響表情。

【點撥】1) contract 作名詞時意為“契約，合同；婚約”；作動詞時意為“締結，訂契約；染上（惡習，疾病等）；（使）收縮，（使）緊縮”。2) frown“皺眉，蹙眉”，既是動詞也是名詞。