A:某固体中加入稀盐酸,产生了无色气体,证明该固体一定是CaCO3
B:某溶液中滴加BaCl2溶液,生成不溶于稀硝酸的白色沉淀,该溶液中一定含SO42﹣
C:某无色溶液滴入无色酚酞试液显红色,该溶液一定显碱性
D:验证烧碱溶液中是否含有Cl﹣,先加稀盐酸除去OH﹣,再加硝酸银溶液,有白色沉淀出现,证明含Cl﹣
如图,P是⊙O的直径AB延长线上一点,点C在⊙O上,AC=PC,∠ACP=120°.(1)求证:CP是⊙O的切线;(2)若AB=4cm,求图中阴影部分的面积.
—Yesterday , my father bought me a new mobile phone as a present , but I don't know how to use it.
—Why not read the ________ first before using it ?