This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Which of these substances need proteins to transport across cell membrane 
Select and explain. 
A. CO2, B. Steroid harmones, C. Vitamin E, D. Glucose
D: Glucose
Answer: D: Glucose 
Explanation: Lipid soluble substances can easily cross membrane. Whereas water soluble substane like glucose needs transporter protein to cross cell memrane.