Final answer:
Since CR and DS are perpendicular to AB and equal in length, they must also be perpendicular to each other, forming a 90° angle, which confirms statement (b) as true.
Step-by-step explanation:
The student's question involves understanding geometric properties specifically related to perpendicular lines. If CR and DS are both perpendicular to AB, and CR = DS, then CR and DS are also perpendicular to each other and form a right angle (90° angle) between each other, which means that statement (b) 'They are perpendicular, forming a 90° angle between each other.' must be true.
This follows from the properties of a rectangle or a right angled triangle, where the sides meeting at a right angle are mutually perpendicular. Given that AB is also perpendicular to both CR and DS, we can infer that AB, CR, and DS form three mutually perpendicular lines, creating a three-dimensional rectangular corner, thus confirming our selection of statement (b).