当太阳活动达到峰值时，其对地球产生的直接影响是（  ）                         

A．干扰某些人造卫星的正常工作和电网的正常输电

B．产生“磁暴”导致全球变暖

C．人们的网上冲浪会受到严重影响

D．北京地区可以在夜晚看到极光

It was my first time I___________ Chairman Hu,and his speech made a deep impression on me.   [ ]

A. saw  

B. see  

C. had seen  

D. have seen