A botanist claims to have discovered a new macronutrient required for plant growth. Most of this scientist's colleagues are skeptical of her claim. Why might they consider it unlikely?

• A. All the nutrients required for plant growth have already been found.
• B. It is very difficult to prove that a plant needs a certain nutrient.
• C. Plants need thousands of nutrients; a new one is not significant.
• D. Plants manufacture their own macronutrients.
• E. Any nutrient needed in large amounts (macronutrient) has probably been noted already.