[译] 我们必须确定一个题目才可以着手写。
[误] We must decide a topic before we start to write.

[正] We must decided on a topic before we start to write.
[注] 表示“（在某事上）作出决定”、“确定”时，decide 是不及物动词，后接on(或upon)。而decide作“解决”解时，是及物动词，后面直接跟宾语。如：Fighting is not the best way to decide an argument.