主要問題是什麼時候開始。

When to start is the main problem.

Source: Tatoeba

Sentence Composition

1 主要 zhǔyào main; principal; major; primary
2 問題 wèntí
  1. question
  2. problem
  3. issue
  4. topic

classifier: 個
=3 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=3 是 shì variant of 是 shì
4 什麼時候 shénmeshíhou when?; at what time?
5 開始 kāishǐ
  1. to begin
  2. beginning
  3. to start
  4. initial

classifier: 個