What of the following is true for all parallelograms? (2 points) a
Opposite sides are parallel.

b
All four angles are congruent.

c
All four angles are acute angles.

d
All four sides are equal in length.

Step-by-step explanation:

a!!

a

Step-by-step explanation:

These are basic properties of parallelograms and there's really no way to explain other than memorizing them.

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.