很高兴为你作答.
① I saw a bird in the tree.（变否定句）
I didn't see a bird in the tree.
③He went to a park yesterday.（变一般疑问句）
Did he go to a park yesterday?
④Amy flew kites last weekend.（向这个句子提问）
When did Amy fly kites?(对last weekend提问)
Who flew kites last wekend?(对Amy提问)
What did Amy do last weekend?(对flew kites 提问)
若有不懂请追问.第一道题为什么用did因为saw是过去式，see变一般疑问句的时候需要用助动词do, 过去式是did,那第二道题为什么要把 went 改掉went是过去式，变一般疑问句用助动词did, 助动词后面跟的是动词原形，所以把went变回go