已知关于x的分式方程$\frac{a+2}{x+1}$=1有增根，则a=____.

根据短文，判断正误。

   Look at this desk. It's Jim's desk. It's brown. Jim's book is on it. It's an English book. His pencil-box is on it, too. His pencil is in his pencil-box. But where's his pen? He can't find it.

下列关于酶的说法正确的是（   ）