— Exactly, _______they've learned a lot about grammar and known many words.
A:so that
B:now that
C:as if
D:even if
设a∈R,则“a=1”是“直线l1:ax+2y-1=0与直线l2:x+a+1y+4=0平行”的( )
宰辅是历代帝王治理国家的辅佐大臣,在古代政治体制中发挥着举足轻重的主导作用,中国古代宰辅制度经历了三个阶段的变化。这三个阶段依此是