Correct Answer: Light

Solution : The correct answer is the third option.

Big: It refers to the physical size or dimensions of an object, not its weight. While something can be big, it may or may not be heavy.

Massive: It also relates to the size or bulk of an object, often implying that it's large and substantial. It doesn't necessarily refer to the weight.

Large: It is similar to "big" and pertains to the size or dimensions of an object. It doesn't specifically describe weight.

In the context of the sentence, the word heavy is used to describe the weight of the truck's load. So, the best antonym is light because it directly contrasts with the concept of weight, indicating that the load is not heavy but rather lightweight.