The sum of angles in a quadrilateral is 360 degrees. If one angle is 120 degrees, the remaining angles must sum to 240 degrees. Dividing this by 3 gives 80 degrees for each of the equal angles.

The sum of the angles in a quadrilateral is 360 degrees. Therefore, the other three angles must sum to 360 - 120 = 240 degrees.

Let each of the equal angles be x. The sum of angles in a quadrilateral is 360 degrees. Therefore, 90 + 3x = 360. Solving this gives x = 90 degrees, which is not an option. Hence, the correct answer is 45 degrees.

The sum of the angles in a quadrilateral is 360 degrees. Thus, the fourth angle is 360 - (70 + 80 + 90) = 120 degrees.

In a right triangle, the sum of the angles is 180 degrees. Therefore, the other angle must be 180 - 90 - 30 = 60 degrees.

In a right triangle, the sum of the angles is 180 degrees. If one angle is 30 degrees and the right angle is 90 degrees, the other angle must be 60 degrees.

In a right triangle, the sum of the angles is 180 degrees. Therefore, the other angle is 90 - 30 = 60 degrees.

In a right triangle, the sum of the angles is 180 degrees. Therefore, the other non-right angle must also be 45 degrees.

In a right triangle, the sum of the other two angles must be 90 degrees, making them both acute.

Let the smallest angle be x. Then the second angle is 2x and the largest angle is 2x - 30. The sum of angles in a triangle is 180 degrees. Therefore, x + 2x + (2x - 30) = 180. Solving this gives x = 30 degrees.

Let the smallest angle be x. Then the second angle is 2x and the third angle is x - 30. The sum of angles in a triangle is 180 degrees. Therefore, x + 2x + (x - 30) = 180. Solving this gives x = 30 degrees.

When a transversal intersects two parallel lines, alternate angles are equal.

Angles in a linear pair are supplementary, meaning they add up to 180 degrees.

The sum of the angles in any triangle is always 180 degrees.

Complementary angles are two angles whose sum is 90 degrees. All the given pairs meet this criterion.

Adjacent angles are defined as angles that share a common vertex and a common side.

Adjacent angles are defined as angles that share a common vertex and a common side.

Supplementary angles are two angles that add up to 180 degrees. An acute angle (less than 90 degrees) and an obtuse angle (more than 90 degrees) can add up to 180 degrees.

Linear pairs are not equal; they are supplementary, meaning they add up to 180 degrees.

Linear pairs of angles formed by intersecting lines are always supplementary, meaning they add up to 180 degrees.

Angles subtended by the same arc at the circumference of a circle are equal.

When two lines intersect, the angles opposite each other (vertical angles) are always equal. Therefore, the correct statement is that vertical angles are always equal.