The iris in the human eye contracts and expands, controlling the amount of light that reaches the retina. what types of muscle control this? a. skeletal and voluntary b. smooth and cardiac c. skeletal and smooth d. smooth and involuntary

The iris is a pigmented muscular curtain found near the front of the eye and between the cornea and lens. It is perforated by an opening known as the pupil. The location of the iris is found in front of the eye lens and the ciliary body and posterior to the cornea. It is bathed in a fluid called as the aqueous humor.

The iris consists of two sheets of smooth muscles with opposing actions: dilation/expansion and contraction/constriction. The primary function of these muscles is tho control the size of the pupil and modulates how much light reaches the sensory tissue of the retina. The sphincter muscle of the iris is a rounded muscle that constricts the pupil whenever there is a bright light, whereas the dilator muscle expands the eye opening when it contracts.

Therefore, the answer is D. SMOOTH AND INVOLUNTARY because first of all the types of muscles that comprises the muscles in the iris are smooth and it is involuntary because they eyes auto-regulates the light that comes to it without our conscious effort.

the correct answer is option b

behavioral response need communication and thus co-ordination at several levels such as interaction among cells, organ system and the entire organism.

behavioral response produces both internal and environmental stimulus.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.