During an Exam, Marta Becomes Stressed Due to a Sawing

During an exam, Marta becomes stressed due to a sawing noise coming from outside the classroom. Primarily, Marta becomes started each time the noise occurs because there is not percievable pattern to why the sound occurs. Which feature of stressful noise is this an example of

A) volume of noise
B) unpredictability of noise
C) lack of control over noise
D) distance from the noise