In a fusion process a proton and neutron combine to give a deuterium nucleus. If `m_(o)` and `m_(p)` be the mass of neutron and proton respectively the mass of deuterium nucleus is
A. equal to `m_(o)+m_(p)`
B. more than `m_(o)+m_(p)`
C. less than `m_(o)+m_(p)`
D. can be less than or more than `(m_(o)+m_(p))`
