Which two options could meet this requirement?

Universal Containers (UC) has large data volumes and is nearing data storage limits. The planned solution is to archive historical data to reduce data storage inSalesforce; however, UC would still like to use reports, queries, and lookups on the archived information.

Which two options could meet this requirement? Choose 2 answers
A . Big objects
B. Custom objects
C. Related objects
D. External objects

Answer: A,D