1道英语语法题It was a game without rules,of which the sole aim see

1道英语语法题
It was a game without rules,of which the sole aim seemed to ___been to drive the ball through the opponent's goal.空白出原句是have,为什么呢?我认为该是has啊,因为前面是“a game”呢
晕了,请教
谢谢，但是我还是不太明白：seemed to后面为什么就要用原型呢？
难道没有someone has been done sth.的句型吗