天然气燃烧放热，如果不计入水的汽化热的热值叫低热值。
参考答案：对
原产地证书应由检验检疫局、贸促会或商务部出具，不能由出口商或生产厂家出具。
— __________ are singers.
— My father is _____. [ ]
A. Tom and Jim's fathers; a singer and an actor
B. Tom and Jim's father; a singer and actor
C. Tom's and Jim's father; a singer and an actor
D. Tom's and Jim's fathers; a singer and actor
