《进口废物批准证书》实行“非一批一证”制度。 ( )
参考答案:对
A number of students ______ playing on the ground but I don't know what the exact number______.
A.are; is
B.are; are
C.is; is
D.is; are
起重作业时必须明确指挥人员,确定联络方式。指挥人员应佩带明显识别标志。()