The answer is A. Urinary system
The state of matter that the particles move independently of one another with very little attraction is, I believe, gas
Weight = (mass) x (acceleration of gravity where the object is)
You didn't tell us WHERE the boulder is, so I have to assume that it's on Mars, where the acceleration of gravity is 3.71 m/s².
675,000 N = (mass) (3.71 m/s²)
Mass = (675,000 N) / (3.71 m/s²)
<em>Mass = 181,941 kilograms</em>
The same weight on Earth would suggest a mass of only 68,807 kg, so you can see how important it is to know where you are when you make your measurements.
The Doppler effect is the right concept to solve this problem. The Doppler effect is understood as the change in apparent frequency of a wave produced by the relative movement of the source with respect to its observer. Mathematically it can be described as,

Here,
= Frequency of the sound from the Whistle
f = Frequency of sound heard
v = Speed of the sound in the Air
Replacing we have that





Therefore the minimum speed to know if the whistle is working is 16.33m/s