A:棉线,因为它比较轻
B:丝线,因为它既轻又不易发生形变
C:铁丝,因为它较重且摆动起来又容易稳定
D:任意选取哪一种都一样,因为单摆的摆动周期仅与摆长有关
(2016•十堰)- I shouted to you at the gate, but you didn't hear me.
- Really? I ____ a telephone call to my mother.
木炭的热值是3.4×107J/kg,6kg木炭完全燃烧可放出 ____ 的热量.若炉中的木炭只剩下0.1kg,它的热值是____ 。