被动语态In 1991, after the Gulf War, Bush’s approval rating reached 91 percent, the highest level

填在哪儿?In 1991, after the Gulf War, Bush’s approval rating reached 91 percent, the highest level recorded since polling _______ (begin) in the 1930s1991年，海湾战争之后，布什的支持率达到91%，这是自1930年的民意测评选票以来最高的纪录。since这里是连词，其后是一个完整的句子：polling ___began____ (begin) in the 1930s填入一般过去时即可，而不用被动（况且你的began是过去式，怎么会和be搭配成为be began呢？）表示“某事物开始”直接用 ...begin，而不是“被开始”比如，上课了：Class begins.而不是Class is bagun.The meeting will begin at nine. 会议将在九点开始。而不是The meeting will be begun at nine.