Question

question 3
scientific research: using human subjects is challenging due to all except:
humans have multiple variables that must be considered
many testing variable are not ethical for humans
humans are available and willing to participate and help the field develop
humans have to abide by the procedures of the study

Explanation:

When using human subjects in scientific research, having multiple variables to consider, ethical issues with testing variables, and ensuring humans abide by study procedures are challenges. However, humans being available and willing to participate is not a challenge but rather a positive factor.

Answer:

C. Humans are available and willing to participate and help the field develop