英语题目：The mobile phone has influenced people's life a

The   mobile   phone  has influenced people's life a lot since it_____                                    (           )

A.invents    B.invented    C.is   invented   D.was   invented

He  ____________ (welcome)  friends from  across  the  world  to  experience   the  "greatness"  of   the   Great   Wall.

Nowadays,computers  _____________(be    used)     in the  classroom    try   to  help  students  learn.

   【第一道题我主要不懂到底选C还是选D.第二道用过去时还是一般现在时.第三道是过去式还是现在时】

   【 希望会做的可以讲解一下,在线等.                                                                                                     】