1.
如图,在正方形abcd中,n为cd的中点,mnꓕcd,cm=2cn,连接bd、ma,ma交bd于点o,则sin∠aob的值为( )
a . 12" style="max-width:100%;vertical-align: middle;">
b . 13" style="max-width:100%;vertical-align: middle;">
c . 32" style="max-width:100%;vertical-align: middle;">
d . 31010" style="max-width:100%;vertical-align: middle;">