The circulatory system and respiratory system are protected by your skin, muscles, and ribs.
<span>The mountains were once seas. The land was forced up by tectonic motion when the mountains were formed. The Sahara also used to be a sea and has a valley full of the fossilized remains of an extinct species of whale. It is generally agreed upon that two plates colliding caused the uplift that created the mountainous zone. Same for the Himalayas.</span>
<span>Homeostasis is the ability to maintain a constant internal environment in response to environmental changes</span>
The answer is d) it encloses specific structures
