11.) What does the $addFields stage do in MongoDB?
12.) Which stage limits the number of documents in an aggregation pipeline?
13.) What does the $unwind stage do in an aggregation pipeline?
14.) Which stage is used to skip a specified number of documents in the pipeline?
15.) Which operator is used in $project to rename a field?
16.) What is the correct order of stages in the aggregation pipeline?
17.) Which stage in the aggregation pipeline is used to join data from another collection?
18.) Which aggregation stage is used to combine multiple documents into a single output document with cumulative calculations?
19.) What is the $expr operator used for in an aggregation pipeline?
20.) Which stage combines documents from multiple pipelines into a single result?