某工程双代号时标网络计划如下图所示，其中工作B的总时差和自由时差（）周。
A．均为1
B．分别为2和1
C．分别为4和1
D．均为4
参考答案：B
活塞的特殊结构设计各有什么优点？
"John does well in school. Furthermore, he takes an active part in the social work. " The logical relationship between the sentences is ().
A. additive
B. adversative
C. causal
D. temporal
