The old man keeps walking around this street. I think he is new here and now he has trouble ____ (find) his way.
12-____=7
7+____=12
____+8=12
近代爱国诗人闻一多在《七子之歌·台湾》中写到“母亲,酷炎的夏日要晒死我了,赐我个号令,我还能背水一战”;台湾爱国诗人余光中于1972年在《乡愁》中写到“小时候,乡愁是一枚小小的邮票,我在这头,母亲在那头”。下列对两段诗歌理解错误的是
椭圆x23+y2=1的焦距为( )