—_______ do you have music lessons?
—Once a week.
A:How often
B:How soon
C:How much
D:How long
下列图示的实验装置或操作正确的是( )
①细胞膜 ②线粒体 ③核糖体 ④中心体 ⑤高尔基体 ⑥内质网
⑦液泡 ⑧叶绿体 ⑨溶酶体.