2. 职称英语
  3. In 1954 Dr. Jonas Salk began______a killed-virus vaccine for polio.A、testedB、ha

In 1954 Dr. Jonas Salk began______a killed-virus vaccine for polio.A、testedB、ha

游客2024-01-02  51
问题 In 1954 Dr. Jonas Salk began______a killed-virus vaccine for polio.
选项 A、tested
B、had tested
C、test
D、testing
答案 D
解析 The verb began needs either an infinitive or a gerund as its direct object; testing is a gerund.
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