请按顺序在下面横线上填上合适的表达式或语句,完成五选一选择器的设计,其中A1、A2、A3、A4、A5都是4位输入总线,Y为4位输出总线,SEL为3位选择端,其功能如下: LIBRARY ieee; USE ieee.std_logic_1164.ALL; ENTITY mux5 IS PORT( SEL : IN std_logic_vector(____________________); --空(1) A1, A2, A3, A4, A5: IN std_logic_vector(3 DOWNTO 0); Y: ______ std_logic_vector(3 DOWNTO 0) --空(2) ); END mux5; ARCHITECTURE bd OF mux5 IS BEGIN PROCESS(______ ) --空(3) BEGIN CASE ______ IS --空(4) WHEN "000"=>Y<= A1; WHEN "001"=>Y<= A2; WHEN "010"=>Y<= A3; WHEN "011"=>Y<= A4; WHEN "100"=>Y<= A5; WHEN OTHERS=>________________________ ; --空(5) END CASE; END PROCESS; END bd;