Q1. A MongoDB aggregation pipeline joins 'users' (100,000 docs) and 'orders' (1,000,000 docs) collections using $lookup on 'userId'. The query runs slowly. Which optimization will most improve performance?

• ○Create an index on 'userId' in the 'orders' collection.
• ○Increase the batch size of the aggregation cursor.
• ○Add a compound index on 'userId' and 'orderDate' in 'users'.
• ○Use $unwind before$lookup to reduce documents.