My car has broken down .和My car is broken down.的区别

My car has broken down .和My car is broken down.的区别
还有两题：8）He__to help the girl .Which one is WRONG?
A.did all what he could .错误 应 把what改为that。WHY?
(4)--what is the weather like here?
---There ———— very little rain.
A.has ; B.has been ; C.are ; have been
PS;答案上说是选B。为什么