Regarding aggregation pipeline optimization concepts in MongoDB, if you have a $sort followed by a $match:

What is a covered query?

In MongoDB, a query ____ consists of a combination of query, sort, and projection specifications.

Regarding indexing and performance in MongoDB, choose the correct statement :

Best describes the concept of Replication in MongoDB ?

Which aggregation option is used to specify the fields that need to be passed to the next stage of the aggregation pipeline?

Describe the best use case for choosing MongoDB map-reduce.

Suppose we have a collection of users with different ages. Which call will find the oldest person with the name John?

Choose the statement that best describes the query below: db.myCol.find().sort({_id:1});

Which is a valid MongoDB document?

Point out the correct statement.