下列合并同类项结果正确的是(        )

竖直放置的两块足够长的平行金属板间有匀强电场．其电场强度为E，在该匀强电场中，用丝线悬挂质量为m的带电小球，丝线跟竖直方向成θ角时小球恰好平衡，如图所 示，请问：

①非金属元素构成的单质中一定存在共价键；②非金属之间形成的化合物一定是共价化合物；③非金属的气态氢化物中一定存在极性共价键；④离子化合物中一定含有离子键；⑤金属元素和非金属元素形成的化合物一定是离子化合物；⑥在一种化合物中只能存在一种类型的化学键；⑦含共价键的化合物不一定是共价化合物；⑧含离子键的化合物一定是离子化合物；⑨氯化钠和HCl溶于水都发生电离，克服粒子间作用力的类型相同．

阅读理解

      Peru(秘鲁)is the fifth largest Latin American country with a people of 14, 430, 000. Almost half of these people live in the city areas(地区). Around Lima, there were 20% of the total (总数) population in 1961. The population here grew faster than anywhere else and in another 35 years reached 1/3 of the total population.

      About 45% of the people are Indians and 50% are white or mixed（混合人种）and the others are Asians, Negroes(黑人)or people from other countries.

      In island areas, only about half of the people can read and write, but at the places near the sea, 2/3 of the people can read and write.