下面这段程序中,clk为时钟信号输入,set为复位信号,y1和y2驱动发光二极管,高电平点亮。set置0,待时钟上升沿,同步初始化;之后set置1,开始运行。则下列说法中正确的是:()。moduleLearn6_2(clk,set,y1,y2);inputclk,set;outputregy1,y2;rega1,a2;always@(posedgeclk)beginif(!set)begina1<=1;a2<=1;y1<=1;y2<=1;endelsebegina1=(~y1);y1=(~a1);a2<=(~y2);y2<=(~a2);endendendmodule
A.y1在时钟上升沿循环亮灭
B.y1保持常亮
C.y2在时钟上升沿循环亮灭
D.y2保持常亮