To determine the best response based on the provided options and the likely content of the graph (which illustrates the composition of the human body), let's analyze each statement:
a. By mass, humans are 2% calcium.
While humans do contain calcium, it is likely a smaller percentage by mass than 2%.
b. Elements making up the human body are mostly potassium and carbon.
While carbon is indeed a significant element in the human body, potassium is not one of the major elements in large quantities compared to others like oxygen, hydrogen, and nitrogen.
c. By volume, humans are 65% oxygen gas.
Though oxygen is a significant element in the body, it generally refers to oxygen in water (H2O) rather than oxygen gas (O2). Typically, the claim about oxygen in terms of body composition refers to its presence in water.
d. Humans are composed primarily of water.
This statement is widely accepted as true. The human body is made up of approximately 60-70% water, which encompasses a significant portion by both mass and volume.
Given these considerations, the most accurate response based on the data shown would likely be:
d. Humans are composed primarily of water.