北京人和山顶洞人有哪些相同之处
①都在北京周口店发现②使用火并吃熟食③长相一样④都有审美观
A．①②③
B．②③④
C．①②
D．①③
答案：C
__________ , some students tend to develop a range of unhealthy habits .
A．Parents don’t watch over them
B．Not having watched over
C．With no parents to watch over them
D．Parents watched over
在测定灰分过程中，煤中矿物质发生哪些变化？
