On putting glass over a lighted candle, the candle flame flickers and produce smoke, why so?

Take two lighted candle A and B, and place them on a table, now put a transparent glass over candle B and see what happens to the candle B, we will observe that candle flame flickers and produces smoke and finally it goes off, this is because on putting glass over it, the air supply was cut off and candle was unable to burn in the absence of air.