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

游客2024-01-02  14

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.
转载请注明原文地址:https://tihaiku.com/zcyy/3328279.html
最新回复(0)