Meileu interior means?

ANSWER: (A) ECFREF: Textbook of biochemistry by G. P. Talwar and L M. Srivastava page 276"La fixit de milieu interior", was coined by Claude Bernard and it means that in spite of ever changing external environment the internal environment remains same.In our body cells are bathed in the interstitial fluid which constitutes the internal milieu. Since interstitial fluid is part of ECF, best possible answer is ECF