下列哪条语句必须在process内部 A. q<=c+d； B. y<=a0 WHEN s=“00” ELSE a1 WHEN s=“01” ELSE a2 WHEN s=“10” ELSE a3; C. WITH s SELECT y<= a0 WHEN “00”, al WHEN “01”, a2 WHEN “10”, a3 WHEN OTHERS; D. CASE din IS WHEN "00" => dout<="00"; WHEN "01" => dout<="01"; WHEN "10" => dout<="01"; WHEN "11" => dout<="10"; END CASE;