面值100元的新版人民币，其正面正下方的数字“100”，采用了光变色防伪油墨印刷，垂直看为绿色，倾斜看为蓝色，防伪油墨中含有MgF₂，其中F的化合价为（　　）

只要朝着阳光，便不会看见阴影。

有位学者说：“中国学术思想最灿烂的时期是秦以前，政治社会最理想安定时期莫过于汉唐。”秦以前“学术思想最灿烂”是指（    ）

单句改错

①Struggled in a world of silence and darkness, Helen Keller seemed to be simple-minded.____

②The three Bronte sisters adopted this practice, Mary Ann Evans did the same.

____

③We decided to fight against this unfair system which prohibits us blacks sitting where we like.____

④Our friendship had developed quickly over the weeks that followed.____

⑤Maybe if I studied science then,I would have been able to give you more help.

____