在比较两种游戏对孩童影响时
原句老师加进了that of的用法
我上网查了一下
还是不太清楚这边是否一定要加进that of或that in文法才正确
想请教版内高手，谢谢!
1.
我:
Childern's emotion after playing LEGO is better than playing online games.
师改:
Children's emotion after playing LEGO is better than that of playing
online games.
2.
我:
The sense of satisfaction in those who played LEGO is lower than those
who played online games.
师改:
The sense of satisfaction in those who played LEGO is lower than that in
those who played online games.

that of = children’s emotions of playing online gamesthan前后比较的东西必须要一致children’s emotion （前句）没办法跟playing onlinegames做比较（后句）

感谢楼上~~~原来如此阿另外想请教that后面的介词，第一句的that of 可以改成that after吗?第2句的that in可以变成that of吗?再次感谢~