一物经凸透镜在光屏上成一倒立等大的实像,则物、像之间的距离为[ ]
A、2倍焦距
B、4倍焦距
C、大于4倍焦距
D、小于4倍焦距
答案:B
---It’s said that scientists have ________ a way to deal with the disease(疾病)
---Really? That’s great!
A.caught up with
B.come up with
C.agreed with
D.compared with
存储器是计算机系统的记忆设备,它主要用来______。
A.存储程序
B.存储数据
C.存储指令
D.上述B)和C)