The brain finds it best to keep smell receptors available for unfamiliar and emergency signals such as the smell of smoke.
句意：大脑发现，最好让嗅觉感受器对不熟悉的和紧急的信号（如烟味）保持可用。
"The brain finds it best to keep smell receptors available for unfamiliar and emergency signals such as the smell of smoke."中真正的宾语是to keep smell receptors available for unfamiliar and emergency signals such as the smell of smoke.