Along with everyone else, we speculated about what "D" could be and later reported some news, via our contributor Green Car Reports, that "D" is an all-wheel-drive version of Tesla's Model S sedan. An AWD Model S is, by the way, what most people think was hiding behind a black garage door with the letter "D" on it in the photo that Musk included with his tweet.
We'll all find out on Thursday when Tesla reveals what "D" is at a media event south of Los Angeles, at SpaceX headquarters (SpaceX is the other company that Musk runs). But here are the top 3 theories:
1. An All-Wheel-Drive Version Of The Model S