I think answer should be A :

Einstein Lead Scoring automatically calculates a score for each lead based on its likelihood to convert.

By placing the Einstein Lead Score component on the Lead Detail page, CK’s reps and analysts can immediately see each new lead’s quality score.

Why Not the Other Options
B. Create a custom score field to capture the marketing Campaign’s quality.
That duplicates what Einstein Lead Scoring already does. You’d then have to build and maintain your own scoring model instead of using the built-in AI scoring.

C. Create a custom object to track the Lead Score and relate it to the Lead.
Einstein Lead Scoring stores scores directly on standard Lead fields. There’s no need for a separate object—just surface the score where users need it.

D. Specify a default score for the leads added to the Campaign.
A default score isn’t based on actual data, so it won’t tell you whether the campaign is producing truly high-quality leads.