A:口腔、胃
B:胃、小肠
C:食管、大肠
D:小肠、大肠
People cut down many trees, __________ many animals are losing their homes.
d=8米,圆的周长是( )
将装有酒精的金属管固定在桌子上,并用塞子塞紧。快速来回拉动绕在管上的绳子,过一会儿塞子跳起来,如图所示。则( )