Many insects have a tough outer shell called an exoskeleton cellulose an endoskeleton chitin

An exoskeleton.

Explanation:

Tough outer shell of many insects is known as exoskeleton that represents an external skeleton. The exoskeleton provides protection and support to the insects body as they lack an internal skeletal system as higher organisms. In insects, it is made up of chitin.

Exoskeleton also plays role in sensing, feeding, excretion, and protection against desiccation in land insects.

Thus, the correct word to be filled in the blank is 'exoskeleton.'

the national environmental policy act (nepa) is a united states environmental law that promotes the enhancement of the environment and established the president's council on environmental quality (ceq). the law was enacted on january 1, 1970. to date, more than 100 nations around the world have enacted national environmental policies modeled after nepa.

what have scientists found to be the most efficient and effective way to insert new sequences into an individual? a-scientists have created genetically altered foods that release dna during digestion. b-scientists use viruses to insert specific gene sequences. c-scientists irradiate genes so that they can be absorbed through the skin.