【单选题】设A={a,b,c},A上二元关系R={,,},则关系R的对称闭包S(R)是()
【单选题】写出 苯甲酸苯酯 的一次硝化的主要产物( )
【单选题】Nowadays traditional pencil tests are still more popular than computer tests because ______.
B.
the charges of the former are smaller
C.
the computer is difficult to access
D.
there are more types of exams in the form. of pencil tests
【单选题】-How tired we are! -Yes. ______we have math tests, _______we have physics tests. So many tests.
A.
Sometime, at other time
B.
Sometimes, at other times
C.
Sometimes, at another time
D.
Sometime, at another times
【单选题】某商场(增值税一般纳税人)实行还本销售家具,家具现售价16500元(含税),5 年后还本,该商场增值税的计税销售额为()。
【单选题】设A={a,b,c},A上二元关系R={(a,a),(b,b),(a,c)},则关系R的对称闭包s(R)是( )