Answer:3.Stack the envelopes neatly and put them in a large bag.
Step-by-step explanation:
An evidence at the scene of crime must be collected with utmost care so as to retain the integrity of the evidence.
A pile of envelope must be collected by collecting the envelopes in a stack form and packing in a large bag so that the sequence of envelopes can be determined. Any kind of bodily fluid must be retained thus it is kept in paper or cloth bag.