增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。

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。

    The students union will organize an activity when we can exchange items we don't need with others. If you are interested it, you can join on Saturday afternoon on the Central Road in our school. As it is known to all, many of us have difficulty deal with used things that mean little to us. If you take it there, not only can you get anything you want, but you can also help others. Beside, it will be a good chance to communicate and make new friend. Any used items is welcome, such as used books, shoes, watches and so on. The more, the good.

若$\theta$是$△ABC$的一个内角，且$\sin \theta \cos \theta =-\frac{1}{8}$，则$\sin \theta -\cos \theta$的值为(    )

在1500米长跑的比赛中，小刚以7.5米/秒的速度跑完前半段，再以5米/秒的速度跑完后半段，到50秒时，小刚跑完____米，到200秒时，他跑完____米