 Issue Analysis:

Products not syncing to Opportunity Products is usually caused by specific CPQ conditions or rules.

 Reasons for Failure:

B: Products with an Effective Quantity of zero are excluded from syncing.

C: Validation Rules on the Opportunity Product object may silently block the sync process if they are not met.

D: Products with a price of zero do not sync by default.

 Why Other Options Are Incorrect:

A: Missing Price Book Entries prevent quoting entirely, not syncing issues.

E: The Exclude from Opportunity checkbox applies to the Product Option, not the syncing process.

 Salesforce CPQ Reference:

CPQ guidelines for syncing Quote Lines to Opportunity Products ​.