--How did the accident happen?

---You know, it ( ) difficult to see the road clearly because it ( ).
A.was,was raining
B.is,has rained
C.is,is raining
D.will be,will rain

--How did the accident happen? How much did she ___in the supermarket? How did you choose the english name? how did... How did you climb to the top of that building? How and Why did the Puritans come to North America? ---How did you find the film yesterday evening? --How did you find the film yesterday evening? How did the early football evolve into its modern form? how did the internet get so popular so fast?