The correct answer for the speed of sound in water at 20°C is option 3, which is approximately 1500 m/s.

Option 1 - 330 m/s: This speed is actually closer to the speed of sound in air at room temperature (around 343 m/s). Sound travels faster in water compared to air, so this answer is incorrect.

Option 2 - 800 m/s: This speed is still slower than the actual speed of sound in water. It is also much closer to the speed of sound in air, so this answer is also incorrect.

Option 4 - 5000 m/s: This answer is way too high for the speed of sound in water. Sound cannot travel that fast in water, so this option is incorrect as well.

In conclusion, the correct answer is option 3, which correctly states that the speed of sound in water at 20°C is approximately 1500 m/s.