Using a balance scale, you are given 8 balls which look identical, but one of the eight balls weighs slightly more than the other seven.

If you are allowed only two weighings on the balance scale, how can you determine which ball is heavier?

a) Place three balls on each side; if they balance, the heavier one is in the remaining two.

b) Place four balls on one side and four on the other; if they balance, the heavier one is in the remaining group.

c) Place two balls on each side; if they balance, the heavier one is in the remaining four.

d) Place three balls on one side and three on the other; if they balance, weigh the remaining two to find the heavier one.