古人的钻木取火的过程是将机械能转化为 能;水力发电是将水的机械能转化为 能;自然界中能量在转化和转移的过程中,能的总量保持 。
内 ; 电;不变
—Liz got the first prize in the speech contest.
—______! She's so shy that she even can't speak in front of her friends.[ ]
A. You're kidding
B. You're welcome
C. Thank you
D. That's nothing
国内航班易登机服务扣减积分多少分/人次?()
A.600
B.1000
C.1500
D.2500