A.Write Concern

B.Indexing

C.Replication

D.Sharding

A.db.posts.find({ likes : { $gte : 100, $lt : 200 } } );

B.db.posts.find({ likes : { $gt : 100 , $lte : 200 } } );

C.db.posts.find({ likes : { $gte : 100 , $lte : 200 } } );

D.db.posts.find({ likes : { $gt : 100, $lt : 200 > > );

A.db.test.insert{"x":2, "y":"apple"})

B.db.test.insert({x:2},{y:"apple"})

C.db.test.push({x:2,y:"apple"})

D.db.test.insert({x:2,y:"apple"})

A.hidden

B.secondary

C.arbiter

D.primary

A.db.posts.createIndex({comments.$.author": {$desc:l>});

B.db.posts.createIndex({comments.author":-l});

C.db.posts.createIndex({commerits.$.author":-l});