单选题：当表示三个一元函数的线性组合时，下列哪种公式写法最符合规范？
当表示三个一元函数的线性组合时，下列哪种公式写法最符合规范？@[C](1)
A. $$a_{1}f(x)+a_{2}g(x)+a_{3}h(x)$$
B. $$af_{1}(x)+bf_{2}(x)+cf_{3}(x)$$
C. $$c_{1}f_{1}(x)+c_{2}f_{2}(x)+c_{3}f_{3}(x)$$
D. $$y_{1}f_{1}(a)+y_{2}f_{2}(a)+y_{3}f_{3}(a)$$
A.$$a_{1}f(x)+a_{2}g(x)+a_{3}h(x)$$
B.$$af_{1}(x)+bf_{2}(x)+cf_{3}(x)$$
C.$$c_{1}f_{1}(x)+c_{2}f_{2}(x)+c_{3}f_{3}(x)$$
D.$$y_{1}f_{1}(a)+y_{2}f_{2}(a)+y_{3}f_{3}(a)$$
答案：C
A. $$a_{1}f(x)+a_{2}g(x)+a_{3}h(x)$$
B. $$af_{1}(x)+bf_{2}(x)+cf_{3}(x)$$
C. $$c_{1}f_{1}(x)+c_{2}f_{2}(x)+c_{3}f_{3}(x)$$
D. $$y_{1}f_{1}(a)+y_{2}f_{2}(a)+y_{3}f_{3}(a)$$
A.$$a_{1}f(x)+a_{2}g(x)+a_{3}h(x)$$
B.$$af_{1}(x)+bf_{2}(x)+cf_{3}(x)$$
C.$$c_{1}f_{1}(x)+c_{2}f_{2}(x)+c_{3}f_{3}(x)$$
D.$$y_{1}f_{1}(a)+y_{2}f_{2}(a)+y_{3}f_{3}(a)$$
答案：C