"Mark, when you think about acquisitions broadly, in what area do you think Facebook needs to buy versus build, basically where do you need external help? And then on VR, a few quick questions. Any update on the shipping delay, how many units shipped in the quarter and expectations for the year? And then also on VR understanding I know it's very, very early, but beyond games and entertainment what verticals, do you expect to be first to utilize VR and AR? Thanks.

Mark Zuckerberg: So on the acquisition philosophy, I mean, I talked about how I think the social ecosystem will play out on a number of these calls. The basic theory that we have is that there are a small number of services that are going to be ubiquitous utilities that 1 billion or 2 billion or more people are going to want to use.

That's core, basic messaging, the core functionality around having your real identity and connecting with all of your real friends and family online. Those are things that we just think are going to be ubiquitous. So we want to build those. At the same time, we also think that there are going to be many, many good businesses and different other social use cases where there are people doing good work and building different companies. We feel no need to own those things. So I think people come up from time to time and suggest should we buy this company or that, and what we look at are what are things that we think are going to be ubiquitous tools and who are the most talented people in the world to build this. When you think about something like virtual and augmented reality, that's how we thought about that.

This is -- those are going to be important platforms over time. It's very early, obviously it's going to take a long time to get there. And a lot of what we felt like we were buying there was a critical mass of the best people and the best technology to go do all the things that we needed to go do over the next 10 years to drive that home and turn that into a big platform.

You asked a question about virtual and augmented reality, what are going to be the big use cases. I mean, for the first few years of virtual reality, I think gaming and video are going to be the big ones. The initial market that we look at are all the people who have Xboxes, PlayStations and Wiis; the people who are excited to have immersive media experiences sitting in their living room for a long period of time and that's a pretty big market. Even though that's not all of what we hope to eventually serve and that's not the full potential of these new platforms, I think that is one case where you can obviously deliver better and richer experiences than what you can with the current generation of technology. Video is going really well. I shared a stat before in some of my comments that on Gear VR alone we're now at more than 2 million hours of video, have been watched in the platform. So that's really exciting. And that, of course, will be bolstered by the fact that these new kind of 360 videos cannot only be watched in VR, so in the headsets, but we're building tools so that you can share them on News Feed and through our products elsewhere as well.

So I think that's exciting. Over time there will be even more. But that I think should be enough to have some initial use. But again, I do want to really emphasize this is early and it's going to take a long time. I think there's a lot of hype around this, and we're just focused on building this to be very good over the long term."