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■In the market, vegetables are sold by ________ kilogram, I mean, by ________ weight. 　　

A. the, 不填         B. 不填, 不填     C. the, the          D. 不填, the　　

答案為A。用介詞by表示度量時，名詞前習(xí)慣上要用定冠詞，如by the kilogram, by the pound, by the pint等，但如果是抽象名詞，則不用定冠詞，如 by weight, by length, by size 等。　　

■When they awake the next morning, they were surprised to find a ________ of fog floating in the air. 　　

A. cover              B. blanket              C. piece              D. mixture　　

答案為B。a blanket of fog 意思是“一片霧”，因為“霧”看上去像blanket，故這樣說，又如：The town was shrouded in a thick blanket of fog. 小鎮(zhèn)籠罩在一片濃霧之中。　　

■Whatever we have achieved, we should always ________ against pride. 　　

A. protect             B. guard             C. defend             D. prevent　　

答案為B。guard against 意為“預(yù)防”，又如：guard against disease 預(yù)防疾病 / They've been doing very well, but they should guard against over-confidence. 他們一直干得挺好, 但應(yīng)防止過于自信。　　

■Since we ________ in driving, we didn't find the trip too tiring. 　　

A. by turns          B. took turns         C. in turn            D. out of turn　　

但從使用的常用性來看，in turn多表示“依次”，by burns 多表示“輪流”，命題者可能就是從這個角度來命題的，所以命題者對此題的答案很可能是A。　　

但事實上，此題答案并不確定，A和C都不能算錯。因為，實際上in turn和by turns均可表示“輪流”（雖然表示此義時in turn不如by turns普通）。如：　　

We did the work by turns. 我們是輪流做這項工作的。——摘自《牛津高階英漢雙解詞典》(1989年第四版)　　

The pictures were lent to each museum in turn. 那些畫輪流借給每個博物館。——摘自《新牛津英語雙解大詞典》