Which is the best way to find the weight of an elephant?

A) gallon
B) ounce
C) kilogram
D) liter

Is it B?

An elephant may weight 10,000 pounds.

A pound is 16 ounces.

16 * 10,000 = 160,000 ounces

Is there a better answer?

a liter?

A liter and a gallon measure volume -- like water or a soft drink.

http://en.wikipedia.org/wiki/Elephant

http://answers.reference.com/information/misc/what_weighs_a_kilogram

My guess would be that its weight would be given in kg or in metric tons

The ounce is the only weight measurement here. Kilograms measure mass not weight. However if this is elementary science they may not know that and would use kilograms for weight.

weight = mass * local acceleration of gravity

To find the weight of an elephant, you would typically use the metric system. The most appropriate unit for measuring weight in the metric system is the kilogram (kg). Therefore, option C) kilogram would be the best choice for finding the weight of an elephant.