极坐标方程$\rho \sin \theta =2\sin 2\theta$表示的曲线为（  ）

增加：在缺词处加一个漏字符号（∧），并在此符号下面写出该加的词。

删除：把多余的词用斜线（＼）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1).每处错误及其修改均仅限一词；

2).只允许修改10处，多者（从第11处起）不计分。

    "Practice makes perfect" was an old saying.It tells us that it does not any matter if we are slow at doing something.As long as we keep on trying and practice,we'll do a good job at the end.The saying is especial useful in English study.Since a student is poor at speaking,he should catch every chance to open mouth and speak English.His oral English may be excellent one day as a result of his hard works.Not only is the saying useful in English study,but it is helpful in our daily life as well.To some degree,it is no easy way in doing everything since the key to succeed lies in "Practice makes perfect".

新中国成立60年来，我国取得了一系列重大的科技成果，请按要求写出重大科技成果的名称。
（1）标志着我国跨入了世界核先进国家行列：____  。
（2）我国开始跻身世界航天科技的大国之列：____  。   
（3）探索生命奥秘具有重大理论意义的发明：____ 。   
（4）实现了水稻育种历史性突破的发明：____ 。

显微镜与开普勒望远镜比较，不同的是显微镜    (    )

 -People in the UK say “football”.
 -Right. But people in the USA say “__________”.