1, because the angle between the direction of the magnetic field and the normal direction of the hemisphere bottom circle is α,

That is to say, the effective component of the normal magnetic field is Bcosα, so the flux is d;

2. Because the magnetic flux is continuous, the magnetic flux entering from above the hemisphere enters from the bottom.

The flux is the same;

3. If the magnetic flux on the whole hemisphere is zero, the upper part is negative.

The lower half is positive; Conversely, the upper part is positive and the lower part is negative.

So it can't be twice. A and C are both wrong. B regardless of the normal direction and magnetic field in this area.

The included angle in the direction is also wrong.

Only d is right.