The danger associated with using carbon dioxide in an enclosed space is（）.

A.on the part of
B.in lieu of
C.subject to
D.in accordance with

A.increased appetite and thirst
B.decreased appetite and thirst
C.gain in weight
D.elevated temperature

A.they generate heat
B.they emit hydrogen
C.of the toxic fumes they emit
D.they recharge faster in a well ventilated space