“由and并列的兩個主語用來指同一個人、同一事物或同一概念時，或是在and并列的兩個可數(shù)名詞前有every、each、no、many修飾時，則謂語動詞用單數(shù)形式。否則就用復(fù)數(shù)形式?！?/p>

A sedentary lifestyle and a changing diet has doubled the number of obses Australians and trembled the army of fat children in the past decade.

■根據(jù)句子的語境，感覺有兩個單詞拼寫錯了：obses→obese（肥胖的），trembled → trebled（使成三倍），即：

A sedentary lifestyle and a changing diet has doubled the number of obese Australians and trebled the army of fat children in the past decade.

■當(dāng) A and B 這樣的結(jié)構(gòu)作主語時，如果是指兩樣?xùn)|西，謂語動詞肯定是要用復(fù)數(shù)。如：

Copper and silver are both metals. 銅和銀都是金屬。

Psychology and economics are social sciences. 心理學(xué)和經(jīng)濟(jì)學(xué)是社會科學(xué)。

Reading and writing are different skills. 閱讀和寫作是不同的技能。

An ax and a saw are the tools of his trade. 斧子和鋸子是他干活的工具。

■如果 A and B 這樣的結(jié)構(gòu)指的是一樣?xùn)|西，或是指同時使用或同時起作用的事物，則可視為一個整體，而連用單數(shù)謂語。如：

The hammer and sickle is the emblem of the Communist Party. 錘頭和鐮刀是共產(chǎn)黨的標(biāo)志。

Drinking and driving is one of the most common causes of traffic accidents. 酒后駕車是導(dǎo)致交通事故最常見的原因之一。

Early to bed and early to rise makes a man healthy, wealthy, and wise. 早睡早起會使人健康、富有，而有智慧。

■比較下面兩句：

To preach and to practise are two different things. 說和做是兩回事。（兩個并列不定式指兩個不同的動作，用復(fù)數(shù)謂語）

To try and fail is better than not to try at all. 嘗試而失敗也比不嘗試好。（兩個并列不定式指一個整體，用單數(shù)謂語）