But I don't think tigers are shut in the cage is good for them.

But I don't think shutting tigers in the cage is good for them。才對

因為妳的句子裏把tigers作為賓語從句裏的主語，首先句義不符合邏輯，其次那樣會使從句裏的主語tigers和謂語is單復數不壹致。