28 In order for a maximum number of boiler generating and circulating tubes to be installed without weakening the tube sheet, which of the listed procedures should be carried out?

A. All rows of tubes should be bent at the same angle.
B. All rows of tubes should be installed horizontal to the drum.
C. Different rows of tubes should be bent to enter the drum at any convenient angle.
D. All tubes should be installed normal to the drum surfaces.