The true statement is:
Composting speeds up the decomposition of organic material.
Composting is a process that uses microorganisms, along with other decomposers such as insects and earthworms, to break down organic material more quickly than it would decompose naturally. The other statements are not accurate. For example, decomposition does not exclusively involve microorganisms, organic material can decompose without composting, and insects generally aid in the decomposition process rather than delay it.