What should the consultant do to solve this issue?

Cloud Kicks has 300,000 account records and 16 million invoices In a custom object with a master-detail relationship to the Account. Each account record takes a long time to display due to the rendering time of the invoice related list.

What should the consultant do to solve this issue?
A . Enable Collapsible Sections for the Invoice related list
B . Move the invoice related list to a separate tab on the Lightning page.
C . Convert the Invoice object into a lookup relationship.
D . Enable indexing on all visible fields on the invoice related list.

Answer: C