Identify the compounds A and B in the following reaction sequence.
`CaC_2(s)+ H_2O(l) to A(g) underset(HgSO_4)overset(H_2SO_4)to B (l)`
A. A is ethylene, B is acetaldehyde
B. A is acetylene, B is propionaldehyde
C. A is ethane, B is ethanol
D. A is acetylene, B is acetaldehyde.