【单选题】His car ______ yesterday, so he can not go to work by car.
【单选题】I’ve arranged ____________ you at the airport, so don’t worry about that.
【判断题】在图( a )所示锯齿波 -矩 形波发生器中,已知 A 1 、 A 2 均为理想运算放大器,其输出电压的两个极限值为 ± 12V ; 二极管的伏安特性如图( b )所示;设振荡周期为 T ,一个周期内 u O1 为高电平的时间为 T 1 ,占空比= T 1 / T 。 判断以下结论是否正确: 振荡频率 f 与输出电压 u O1 的幅值无关;
【单选题】The reason why we were so late is________
A.
because of the car’s breaking down
B.
That the car breaking down
C.
because the car broke down
D.
that the car broke down
【判断题】建群种是对群落的结构和群落环境的形成有明显控制作用的植物种。