针叶树种、阔叶树种两类中对土壤有利的是（）类。
参考答案：阔叶树
Which of the students _____ the examination? [ ]
A. not pass
B. didn't pass
C. pass
D. didn't passed
设有如下关系表：
则下列操作正确的是( )。
A．T=R/S
B．T=R×S
C．T=R∩S
D．T=R∪S
