This is Mary's and Tina's desk.改错

This is Mary's and Tina's desk.改错
This is Mary's and Tina's desk.改错

This is Mary's and Tina's desk.改错
更正：This is Mary and Tina's desk.
Mary and Tina's 表示“玛莉亚和蒂娜共有的桌子”.而Mary's and Tina's desks 表示他们两个分别的桌子,这里的desk要用复数形式.