唐朝由盛转衰的转折点是( )
A:安史之乱
B:藩镇割据
C:宦官专权
D:黄巢起义
在△ABC中,AB=AC,∠B=54°,则∠A=____°.
某公司为了开发新产品,用A、B两种原料各360千克、290千克,试制甲、乙两种新型产品共50件,下表是试验每件新产品所需原料的相关数据:
Mary _________ really hard on his book and thinks he'll have finished it by Friday.