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 the following has growth hormone stimulating activity? 
Select and explain. 
A. IGF-1, B. Somatostatin, C. REM sleep, D. Ghrelin
D: Ghrelin
Answer: D: Ghrelin 
Explanation: None