下面属于可再生一次能源的是（）。
A.地热能
B.水力
C.煤炭
参考答案：B
At first I regretted _____ them to stay, but we soon became great friends.
A．to invite
B．invited
C．to have invited
D．inviting
在发射光谱分析法中选择内标元素和内标线时应遵循哪些基本原则？
