The main uses of when are:
 Question word:
When did you last see your father?
 Relative word:
I cannot recall an occasion when he asked me for help before.
 Subordinating conjunction introducing a noun clause:
I haven’t told them when I start.
 Subordinating conjunction introducing an adverbial clause of time:
The off-season hotel had been empty when she arrived.
For Scientific english editing and Medical Writing Services visitwww.manuscriptedit.com
