根据短文内容及首字母提示补全单词

Let me tell you something about our park. It’s not very big b  1 beautiful. Here’s the g 2 . We can go into the park form here. on the l  3 of it. There are two toilets. There is a c  4 on the right.  We can drink coffee or have meals there.  There is a big tree near it. in the tree, there are many b 5 . they are singing. In the m  6  of the park, there is a p  7  . There are many boys and girls on it. Some are flying kites, and others are dancing. They are h_ 8 _. Near the playground, there is a nice and big l _9__ . There are many b  10  in it, and we often read them there. 

渐开线齿轮机构的高副低代机构是一铰链四杆机构，在齿轮传动过程中，该四杆机构的（）。

A.两连架杆的长度是变化的；

B.连杆长度是变化的

C.所有杆件的长度均变化；

D.所有杆件的长度均不变