Which estimator will consistently have an approximately normal distribution? a. proportion b. median c. standard d. deviation range

Estimator is the rule for calculating estimation. 
The normal distribution is the most important and most widely used distribution in statistics.
The normal curve is symmetrical about the mean μ;The mean is at the middle and divides the area into halves;The total area under the curve is equal to 1;The Normal (Gaussian) distribution is completely determined by its mean and standard deviation σ (or variance σ2). 
The median estimator has an approximately normal distribution.