A:is easy to look after
B:are easy to look after them
C:are easy to look after
D:is easy to look after it
细胞在生长过程中,当细胞体积逐渐变大时,表面积与体积之比( )
读课文《鸟儿的侦查报告》根据意思写词语。
①浓厚而带粘性。____
②环境中混入了有害物质。____