It's sunny on launch and you're ready to take off, but the wind has been from the back for quite a while. What do you do?
Gliders suffer the most from direct sunlight. The airtight coating is damaged by the UV-radiation. Don't leave your glider out in the sun unnecessarily.
Additionally, sitting on the reserve parachute may damage it without you noticing, so it might fail if you ever need it. Never sit on your harness.
Which data do you need to calculate the wing load?
The wing load is defined as the weight on the wing per square metre. Therefore you need the total take-off weight and the flat surface of the wing to calculate it. For example, a 25m2 glider flown by a pilot with a TOW of 100kg has a wing load of 4kg/m2.

What are the minimum requirements for a safe take-off?
A straight headwind is not necessary, you can take off in a slight crosswind. The runway should be clear of cables and other obstacles, but a 500m radius is not necessary. It is however essential to be able to abort your launch, for example when you notice a knot in the lines.
Standing on launch you see a rain shower approaching. Do you take off?
D is the only safe answer. You can never be sure that you have landed before the rain arrives, so C is risky. B is only partly true for light rains, but again you're taking a risk. A is not true, although flying in cloud is illegal in many countries.

How tight do you need to pull the leg straps of the harness?
The tightness of the leg straps does not influence the flying properties of the paraglider.
When the leg straps are too loose, after take-off you will find yourself hanging low under the seat and it's more difficult to get in the harness.
Too tight will hinder your movements during take-off, depending on the harness design. In some harnesses it will prevent you from getting into the seat fully.

You're on a straight course and you don't need to change direction any time soon. What do you do with the brake handles?
Modern paragliders fly best without any brake applied - at the so-called trim speed.
But by applying a little bit of pressure, you take out the slack in the brake lines. You feel better what the wing is doing and you can react quickly and subtly to keep the wing straight overhead. This is called active flying.
If you have some more experience it doesn't hurt to let go of the brake handles and relax, but only if it's safe to do so.

How tight does the chest strap of the harness need to be?
A short distance beween the karabiners results in a stable flight but enhances the risk of twisting, for example after a collapse.
A large distance between the karabiners results in a higher sensitivity to weight shift but also to more dynamic reactions of the paraglider.

A pre-flight check should be executed...
Before you take off, you should check at least these things: pilot, lines, canopy, wind, airspace.

Which pre-launch check is the most important?
Even though all newer harnesses have a safety feature to prevent you from falling out of the harness if you forget your leg straps, this is very uncomfortable and on an older harness it may be a fatal mistake. Checking lines and canopy is of course very important as well.
See the section on Launching in the Basic techniques chapter.

What do you do when you can't hear the instructor over the radio during a flight?
B is correct, A and C are nonsense of course.
Answer D is the second best choice in case your mind goes blank, you panic and you don't know what to do. It's better to do nothing in that case.
Your result is shown above.