《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。（）
