The addition of the 500 lb baby elephant will have a huge impact on the mean, since you'll be finding the average (adding all numbers then dividing). So the only logical answer would be the chosen. The median will most likely either decrease or stay the same, but since staying the same isn't an option for the median, it's most likely going to be decrease.
[I do apologize in advance if it's wrong, and next time try submitting work on time :)) Hope I helped!]
