科学家用15N的硝酸盐作为标记物浸泡蚕豆幼苗，追踪蚕豆根尖细胞分裂情况，得到蚕豆根尖

请仔细阅读四段话，从A、B、C、D中找出对应的小标题，并回答第5小题。

小题1:No one wins all time. Learn from the times that you lose. All great champions were once losers at some point. But, they learned. And they kept a positive attitude until they got better.

小题2:Your happiness is up to you. Many people forget this. Truly successful people choose happiness no matter what their present situations are.

小题3:Chances lie in what you do every day. You do the same work. You eat the same foods. You wear the same clothes. Try a new way. Take a new path. Even talk to someone new.

小题4:Opportunity is everywhere. Even the worst situations have opportunities. Seize（抓住）the opportunity, and seize the time. That’s the secret of success.

小题5:The material above tells us the ways to ______

A．find a good job

B．live a positive life

C．protect the environment

D．keep us healthy

分程控制系统中两个阀的信号范围分段由（）实现的。

“使其言而是，则智者所见略同”中，“是”的意义是（）

A.这样

B.这些

C.是这样

D.正确

E.认为正确

花粉在萌发过程中产生花粉管，当花粉管进入（　　）时释放出精子．

A．柱头

B．花柱

C．子房

D．胚珠

Windows 2000支持长文件名，但最长不能超过______。