A:欧文顿
B:罗伯特森
C:桑格和尼克森
D:施旺和施莱登
① 画射线DA;
② 画直线CD;
③ 连结AB、BC;
④ 延长BC,交射线DA的反向延长线于E.
Linda needn't________her parents any more—she could be entirely independent by working as a nurse.