A:①②③④⑥
B:③⑤⑥
C:①②④
D:④⑥
Teenagers should ________ to take care of themselves from a young age.
What's the relationship(关系) between the two speakers?
①转动粗准焦螺旋,使镜筒上升 ②转动粗准焦螺旋,使镜筒下降 ③左眼注视目镜
④来回转动细准焦螺旋使物像清晰 ⑤物镜接近玻片标本 ⑥出现物像.