The number of students in our school ____about 30,000 and ______them study hard.

A．is; a large amount of

B．are ; a number of

C．are ; large amount of

D．is ; a large number of

有机磷酸酯类严重中毒时的症状（）

A.M样状

B.N样症状

C.a样作用症状

D.中枢神经系统症状

E.M、N样症状及严重的中枢神经系统症状