Which of the following will not allow users to create an account?

Meteor’s automatic handling of optimistic UI, if a method unexpectedly fails the optimistic changes will roll back and the Minimongo database will end up in a consistent state?

This data model works pretty well, But it has an one major weak point. Which of the following do you think it is? { "_id": "one", "text": "Meteor - Full Stack Javascript Platform", "parent": null } { "_id": "two", "text": "Why do you say so?", "parent": "one" } {{each getComments}} {{text}} {{if haveChildren}} {{> comments}} {{/if}} {{/each}} Template.comments.helpers({ getComments: function(){ var parent = this._id || null; return Comments.find({parent: parent}); }, haveChildren: function(){ return Comments.find({parent: this._id}).count() > 0; } })

To change the values of a document without deleting it first, use the __ operator. This operator will only change the values of the specified fields without affecting the rest of the document?