曲柄连杆机构是发动机实现工作循环，完成能量转换的主要运动零件。
参考答案：对
Americans eat____ vegetables per person today as they did in 1990. [ ]
A. more than twice
B. as twice as many
C. twice as many as
D. more than twice as many
考察可选方案的优缺点，再按照前提和目标来权衡（）
A.可预测的投入与效益之比
B.选定方案
C.比较方案
D.执行方案
E.编制方案
