指出下列那些运算是二元运算( )<br>·在整数集<img src="/lqwvjeImg/a7/a748fdfd539b893dd661338e2e3310ed.png">上,<img src="/lqwvjeImg/89/89796c156f0e9a05b27218aebd685b96.png">;<br>·在有理数集<img src="/lqwvjeImg/81/81d611787f081d0d797adf6827ab766d.png">上,<img src="/lqwvjeImg/1a/1aa96249a159bfdcb70e35116b519da7.png">;<br>·在正实数集<img src="/lqwvjeImg/db/dbebf5ba79cd446d98d37daf29f6b5bf.png">上,<img src="/lqwvjeImg/13/1338de4a02abebf9d639e1a92db5e62b.png">;<br>·在集合<img src="/lqwvjeImg/d8/d82309d0bdaf9349857bb4bd1c9c3847.png">上,<img src="/lqwvjeImg/68/6811c2e9b59a0dfc6bf36da9f40f35c1.png">。