[D_(2)O" is preferred to "H_(2)O," as a moderator,in nuclear reactors "],[" because "],[" (a) "D_(2)O" slows down fast neutrons better "],[" (b) "D_(2)O" has high specific heat "],[" (c) "D_(2)O" is cheaper "],[" (d) The neutron absorbing ability of "D_(2)O" is higher "]