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;