Which two methods should the developer use to avoid this error?

A developer encounters APEX heap limit errors in a trigger.

Which two methods should the developer use to avoid this error? (Choose two.)
A . Use the transient keyword when declaring variables.
B . Query and store fields from the related object in a collection when updating related objects.
C . Remove or set collections to null after use.
D . Use SOQL for loops instead of assigning large queries results to a single collection and looping through the collection.

Answer: A,D