设H,K是群(G,<imgwidth="11"height="11"src="http://wljy.whut.edu.cn//uploadfiles/word/lsss002.files/image028.png">)的子群,下面代数系统是(G,<imgwidth="11"height="11"src="http://wljy.whut.edu.cn//uploadfiles/word/lsss002.files/image029.png">)的子群的是( )
①
(H∩K,<imgwidth="11"height="11"src="../uploadfiles/word/lsss002.files/image028.png">)
②
(H∪K,<imgwidth="11"height="11"src="../uploadfiles/word/lsss002.files/image028.png">)
③
(K-H,<imgwidth="11"height="11"src="../uploadfiles/word/lsss002.files/image028.png">)
④
(H-K,<imgwidth="11"height="11"src="../uploadfiles/word/lsss002.files/image028.png">)