In this question, we need to find which molecules are considered to be nonpolar, let's analyze each one of the options:
Butanoic Acid is considered to be similar to oil, therefore is slightily soluble in water but more soluble in nonpolar substances, therefore can be considered nonpolar
Carbohydrates are considered polar, being able to dissolve in water, this is due to the OH functional group in the molecules
Muscles, this is not easy to answer, since muscles are composed of many compounds, therefore this one in specific I can't say if it's one or another
Proteins can have a strong nonpolar side chain, making it similar to oil in water, nonpolar
Cell membranes, another case in which the answer is not clear, since a regular cell membrane has both polar and nonpolar parts