No one knows how the huge rocks _______ and _______ without our modern machines eight hundred years ago.
A:were cut; moved
B:were cut; move
C:are cut; moving
D:are cut; moved
如图所示,有一轻质木板(质量忽略不计),左端可绕O点转动,长为L,右端放一重为G的物块,并用一竖直向上的力F拉着.当物块向左匀速滑动时,木板始终在水平位置保持静止,则下列表示拉力F与物块运动时间t的关系图中,正确的是()
假如你有机会去埃及观看金字塔,你听到的当地语言是
如图是某生态系统部分生物的营养关系图解.请回答下列问题:
He's under stress because he has too much work to do.
读“亚洲范围图”,回答问题: