【正确答案】 B

【答案解析】[解析] raise the yield by 40%“将产量提高了40%”，这是增加或减少多少的倍数表达法。如果要表达的是纯增加或减少的具体数，就用介词by表示(有时by可以省略)。如：raise the price by 10%；The price of tea has risen by five pence. Party membership has increased by 4,000. Butter rose five cents in prices.如果纯增加或减少的量刚好是整倍数时就不需用介词by，如：Foreign investments increased six times.如果要表示“增加到或减少到……”则需用介词to；如果要表示“(从……)增加到(或减少到)……”，就要用(from…)to，如：The price of tea has risen (from 20 pence) to 30 pence.