What approach should an architect recommend that conserves API limits?

A system at Universal Containers needs to retrieve opportunity details(including line items and opportunity learn) and then update the opportunity with new information in real time, as one atomic operation.

What approach should an architect recommend that conserves API limits?
A . Use a publisher action to update the data and callback to the other system.
B . Use the generic streaming API to publish changes and listen for updates.
C . Use the SOAP API to upsert the data. The API will then return all opportunity details.
D . Use a custom Apex class with a webservice method that performs both actions.

Answer: D