下列描述不属于星型拓扑的优点是（    ） A.
易于实现 B.
易于故障排查 C.
易于网络扩展 D.
易于实现网络的高可靠性

单项选择题They only have limited amount of time to get their points across.A.largeB.totalC.smallD.similar

单项选择题Which of the following is the possible risk in using nano-materials mentioned in the passaA They may cause some damage to the body cells.B They are harmful materials themselves.C They may store in the body.D They may behave differently in the body and the environment.