Final answer:
An angle change less than 90° is called an acute bend. The term 'critical angle' relates to optics and the minimum angle of incidence for total internal reflection, not the question asked.
Step-by-step explanation:
A single change in direction of less than 90° is known as a(n) acute bend. Therefore, the correct answer to the question is B) Acute bend. An acute angle is defined as an angle that is less than 90°. A right-angle bend corresponds to exactly 90°, an obtuse bend represents an angle greater than 90° but less than 180°, and a reflex angle is greater than 180°.
It's important to note that the term 'critical angle' relates to optics and is the angle of incidence that results in an angle of refraction of 90°. When the incident angle equals the critical angle, total internal reflection occurs, preventing the light from passing into the surrounding medium. This concept is associated with the phenomenon where a light ray is reflected back into a material at a certain Minimum Angle Of Incidence, known as the critical angle.