Which of the following characteristics is mainly responsible for diversification of insects on land?

Exoskeleton is mainly responsible for diversification of insects on land.

Unlike vertebrates, an insect's supporting skeleton is located on the outside of its body.  

It not only gives shape and support to the body's soft tissues, but also provides protection from attack or injury, minimizes the loss of body fluids in both arid and freshwater environments, and assures mechanical advantage to muscles for strength and agility in movement. 

The exoskeleton can resist both physical and chemical attack. 

It is covered by an impervious layer of wax that prevents desiccation. 

Muscles that attach directly to the body wall combine maximum strength with near-optimum mechanical advantage (leverage).