当归挥发油中主要含有 。
A. 蒎烯
B. 藁本内酯、正丁烯基酰内酯
C. 柠檬烯
D. 阿魏酸
Bob hasn’t finished the report yet, but he promised _____ it ready tomorrow afternoon.
A. to have
B. have had
C. having
D. has
I still remember _____ to the man who we later knew was the sales manager of the company.
A. to be introduced
B. being introduced
C. having introduced
D. to have introduced
When he saw Jane fall down on the ice, he couldn’t help _____.
A. laugh
B. laughs
C. to laugh
D. laughing
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