21.The design of the waste-heat boiler heat transfer surface is largely a problem of convective heat transfer, and in principle is the same as for the oil-fired boiler designs, except that the intertube radiative conductance will be so low that it can be neglected. Based on this description, which statement is false? (A) The intertube radiative conductance in a waste-heat boiler is an important factor to be considered. (B)The convective heat is a significant problem for evaluating the heat transfer surface in a boiler. (C)The intertube radiative heat is negligible due to its relatively low value in a waste-heat boiler. (D)The design of the waste-heat boiler heat transfer surface is the same as the design of oil-fired boiler in principle.