It is Saturday morning. The sky is blue. My father and I are going to the park. There are a lot of people in the park. Some children are running on the grass. A dog is running after them. Some men are sitting on the grass. They are talking. Two girls are flying a nice kite. Three women are standing under a tree, and they are watching the children playing. There is a boat in the lake and two women are boating. Everyone in the park is very happy.

函数$f\left(x\right)=\sqrt{-x^2+2x+3}$的单调递减区间是 （  ）

C、N、O、Al、Si、Cl、Fe是七种常见元素