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A question on the volumn shown in trading platform

I notice that the volumn shown is a sum of all B & A volumns. But in a trade, if someone Ask to sell  at a price, there must be someone Bidding to buy at that  price too and the trade concludes. So why does it show the B & A when i click on the " Time & Sale" in my trading platform?

Very confused...newbie here...appreciate if someone can enlighten me. Thanks.

Time	Last	Volume	Bid/Ask
15:47:04	105.160	200	A
15:46:17	105.160	200	A
14:49:07	105.160	600	B
13:59:01	105.160	100	B
12:16:35	105.160	100	B
09:24:10	105.200	500	A