This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
All are ectodermal in origin except 
Select and explain. 
A. External acoustic meatus, B. Anal canal, C. Sebaceous gland, D. Bone marrow
D: Bone marrow
Answer: D: Bone marrow 
Explanation: Human embryology; 10th edition; Inderbier Singh; Page no 95 Derived from ectoderm Epithelium of skin, hair follicle, sweat gland, sebaceous gland, mammary glandEpithelium over cornea and conjunctiva, external acoustic meatus, outer surface of the tympanic membraneSome pa of the mouth, the lower pa of the anal canal, terminal pa of the urethra, female external genitalia