In a Worship Service for the Hindu Deity Ganesh,when and Why

In a worship service for the Hindu deity Ganesh,when and why is an Aarati performed?

A) At the beginning,to focus the worshippers' thoughts
B) At the beginning,to invoke several related deities
C) In the middle,to transition into the faster second half of the service
D) At the end,to atone for any mistakes made during the service
E) At the end,to purify all worshippers present at the service