Why each Ember data transaction sends two separates requests to server?

I am using ember data in my app, however, I realise that Ember data will make two seperated requests (for example an GET and an OPTIONS) to server which of course takes a longer time than making a single request.

See screenshot below, the OPTIONS requests take 1 second to complete and total 2 seconds for each user operation.

My question is why it makes two requests? and is this necessary to make an OPTIONS request? If not how can I stop let my Ember data making OPTIONS request?