若函数f（x）=$\left\{\begin{array}{c}{x}^2+ax-2,x\le 1\\ -a^x,x>1\end{array}\right.$（a＞0，且a≠1）在（0，+∞）上是增函数，则a的范围是（　　）

赤潮是哪种污染的标志？（    ）。

根据短文理解，选择正确答案。

    There are fifty students in our class. There are twenty-four boys and twenty-six girls. Some students live near the school, and some others live far from school. About half of the students usually come to school by bike. They often get to school at a quarter to seven. About fifteen students often come to school by bus. They often get to school very early, too. Another ten students come to school on foot. Their homes are near the school, but they are often late for school, because they get up late.

请回答以下问题：

毛细血管出血后会自行凝固，主要是因为血液中有血小板。（判断对错）