1．Did you see Xiao Li at the party?

1．Did you see Xiao Li at the party?--No,_______by the time I arrived.为什么填she‘d left而不是she must leave?2 They have been in the library since_______为什么填eight o‘clock不填it had been open?3.Return the tools to_______ gave them to you.为什么用whoever不用whomever4.The tigers in the zoo are heavy,_______is more than 200 pounds.为什么填the biggest of which不用which.5.Do you remember the day when we first met.可不可以改成 Do you remember the day which we first met on.6.In order to protect the environment,we are not allowed_______ the waste as we used to为什么用to burn up 不用burning up,不是有allow doing 、allow sb to do么