从物质循环的观点看,人体中碳元素究其根源来自( )
A:食物中的碳
B:有机物里的碳
C:大气中的二氧化碳
D:非生物环境中的碳
下列标点符号使用有错误的一项是( )
What's this? ____ Her name is Li Li.
Hello, Jenny.____ I'm fine.
What's her name?____ I have four.
How many books do you have?____ It's a cat.
How are you?____ Hi, Wang Hong.
下列各组物质中全部都属于纯净物的是