【单选题】He a worker in a factory, but he a pop star two years ago.
A.
used to be; has become
C.
was used to be; becomes
D.
was used to being; has become
【判断题】因为晶体三极管由两个PN结组成,所以晶体三极管可以当同材料的晶体二极管使用。
【判断题】因为晶体三极管由两个PN结组成,所以晶体三极管可以当同材料的晶体二极管使用。()
【判断题】因为晶体三极管由两个PN结组成,所以能用两个晶体二极管反向连接起来当晶体三极管使用。()