This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to ollie
Stand on the board.
Get a good feel for its shape, the tightness of your trucks, and the size of your wheels. Ollies are always easier on a familiar setup.

Available options:
(a). For a four wheel run, you'll want to come down and jump onto the board with your trucks. If you prefer two wheel runs, try to have your trucks have significant traction..
(b). A board with tightly packed trucks can be difficult to ollie on. Some builders, like blue whitehead, have different shaping styles..
(c). Do not lean forward or to the side! Let the bike stay in front of you. Many riders find it easier to look over the handlebars during a ollie when they're wearing helmets and safety gear..
(d). If your trucks are too loose and you can't keep in control while crouching, then tighten them until things are a bit smoother. Adjust your feet with your front foot near the middle of the board and your back foot on the tail of the board..
The answer is:
(d).