下面是一名学生所做的4道练习题：①﹣2²=4②a³+a³=a⁶③4m^﹣4= $\frac{1}{4m^4}$ ④（xy²）³=x³y⁶，他做对的个数（   ）

我国的“神舟五号’，载人飞船己发射成功，“嫦娥”探月工程也己正式启动．据科学家预测，月球的土壤中吸附着数百万吨的 ${}_2^3$  He，每百吨 ${}_2^3$  He核聚变所释放出的能量相当于目前人类一年消耗的能量．在地球上，氦元素主要以 ${}_2^4$  He的形式存在．下列说法正确的是（   ）

A)信息归纳    An important event that I remember well was the Indian Ocean earthquake and tsunami（海啸） that happened on December 26^th, 2004.The earthquake happened under the sea and caused a tsunami that killed many people and destroyed many places in different countries.
    When I heard the news of the earthquake and tsunami, I was hanging out at my classmate's house with my friends. My friends were eating snacks and playing computer games.
    I remember this event well because my mother was in Phuket（普吉岛）, Thailand at the time for her job,and Phuket was one of the places affected by the Tsunami.I was so worried and afraid that I cried. I went home immediately and waited for hours with my friend before we received the news that my mother was alive and safe.
Information Card

What was the event（事件）？	⑴____
When did the event happen?	⑵____
Where was the writer's mother when the event happen?	⑶____
What was the writer doing when the event happened?	⑷____
Why was the writer's mother in Thailand?	⑸____

△ABC中，∠C=90°，∠A=60°，AC=2cm．长为1cm的线段MN在△ABC的边AB上沿AB方向以1cm/s的速度向点B运动（运动前点M与点A重合）．过M，N分别作AB的垂线交直角边于P，Q两点，线段MN运动的时间为ts．

判断句子是否正确。