Which of the following expressions can not be used with aggregation?

Best statement that describes: 'why aggregation queries outperform mapreduce for small datasets'.

What is the maximum number of Indexes per collection allowed?

What is the maximum size of an Index key?

Regarding storage in MongoDB, which is incorrect?

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

For the query below db.collection.find( { x: 5 } ).sort( { z: 1} ) Choose the best index to support the query

Choose the type of query where indexes can result in slower query response time.

Given the below statement, please choose the most probable reason:- 'You have a web application with mongodb as a backend. A query returns a resultset, however when called a second time the result set is empty.'

Which is correct index types?

What is the minimum nodes required for replica?