Answer:
Drop each ball from the platform three more times
Explanation:
Reliability or precision means how much the measured values vary from each other when measured by performing the same experiment repeatedly.
When measuring values by observation in physical experiments of this nature, it is best to perform the experiment and measure the values at least three times. The more the better.
In such measurements there is always a margin of error, e.g how at exact time you start and stop the stop-watch. There may also be a but harder or softer side of ball (tennis ball strip) touching the ground. In order to minimize such and some other margin of errors, it is advisable to measure the values more than 3-4 times, and then take their mean. The value now obtained would be would reliable or precise.
Second and third options are incorrect because they will have no effect on improving the reliability.
In order for the fourth option to be correct, the other people need to do the same (not similar) experiment, with the same balls and same conditions/instruments. That would be equivalent to repeating the experiment 3-4 times, which is already covered by first option.
