联锁系统除应进行分项试验外，还应进行（）试验。
A、回路
B、系统
C、整套联运
D、A、B、C
参考答案：C
According to the passage, all the following are easier to synthesize EXCEPT ______
A．aromatic ingredient in vanilla
B．vanilla
C．aromatic ingredient in wild cherry
D．the flavor of fresh coffee
