The correct option is
C Nephrons of mammals
In mammals the excretory organ is Kidney. The nephron is the structural and functional unit of the kidney. The body of the nephron is divided into renal corpuscle (Glomerulus and its surrounding Bowmans capsule), Proximal convoluted tubule( PCT), Henle's loop and Distal convoluted tubule( DCT). Hence, Henle loops occur in nephrons of mammals.So, the correct answer is 'Nephrons of mammals'.