Answer:
Option d is right
Step-by-step explanation:
Given that In an experiment to determine the acceleration due to gravity, one student drops a tennis ball out of the school’s third floor window. Another student starts a timer when the first student lets go and stops the timer when the ball hits the ground. They conduct the experiment once
Because only once may be biased by pushing the object or due to air or some other reason.
Hence to get accurate results there must be repitition of trials.