[单选题]
The horizontal component of the7f2 0iylj7tnl r dcj2. buttressing force at the base of a po:3bsku0rj-ru:s lv;adc z iuw3:jj3 + /9xwj iinted arch j jr /aj +l9-ww0 u3rxvku3ibiud3j;::sz:c sis
A. less than that of a rounded arch.
B. equal to that of a rounded arch.
C. greater than that of a rounded arch.
D. zero in magnitude.
