a bag还是an bag?为什么?

a bag还是an bag?为什么? an opp bag 还是 a opp bag? a small red bag 还是 a red small bag? 是school bag 还是bag a bag This is a bag.( )bag is yelloy.填什么为什么? 请问a type of small bag中的bag为什么不可数? What color is your bag?It's____yellow bag.A.a B.an C.the D./ What is this in english?A This is a bag B It is bag C It is a bag 为什么 what are these in a black bag?还是what are there in a black bag? there a lot of junk food in the bag是填is 还是are为什么 the corner of后面加bag的话bag前面用a 还是the? This bag is heavy.That bag is a little ）A heavier B heavy 为什么 I have a bag. a bag lady a bag of rice A bag of b_____. a bag of wind