A:making; would study
B:to make; was studying
C:to make; had studied
D:making; had been studying
人类早期的文明最早诞生在亚非的大河流域。右图是哪个古代文明的发源地( )
4Al(s)+3O2(g)=2Al2O3(s) ΔH1
4Al(s)+2O3(g)=2Al2O3(s) ΔH2
3O2(g)=2O3(g) ΔH3则( )
阅读下列材料,然后回答问题.在进行二次根式的化简运算时,我们有时会碰上形如23+1的式子,其实我们还可以将其进一步简化:23+1= 23-13+13-1= 23-132-12=3﹣1.以上这种化简的步骤叫做分母有理化.
请用上面的方法化简:12-3.