1. One thing is certain -- the balance of nature on this water planet is easily upset.
    有一点是可以肯定的- 这个有水的行星上的自然平衡是十分脆弱的。

2. One group performed balance exercises on a computer-controlled platform once a week, one group took a weekly tai chi class, and a control group met for a weekly discussion.
    一组每周在电脑控制的平台上进行一次平衡练习，一组每周上一次太极课，而另一受控组则每周进行一次讨论。