A:has waited
B:was waiting
C:waits
D:is waiting
下列地区人口分布比较稠密的是
根据上下文提示补全对话。
A: What's on the farm?
B: ____ ____ a lake and some trees.
A: Is the farm ____?
B: Yes, it's very big.
A: ____ ____ an elephant on the farm?
B: Yes, there is. It's very strong.
A: Is there a house?
B: No, there ____.
下列各图中,已标出电流I,磁感应强度B的方向,其中符合安培定则的是( )