Final answer:
Massachusetts is the state that encompasses the Charles River, Connecticut River, and Merrimack River, all of which have been important for the state's development and history.
Step-by-step explanation:
The state that has the Charles River, Connecticut River, and Merrimack River is Massachusetts. These rivers have played a significant role in the history and development of the region. The Charles River flows through several Massachusetts counties, eventually spilling into Massachusetts Bay. The Connecticut River, while it spans several states, also runs through Massachusetts and was pivotal in the establishment of various settlements by colonists such as the Reverend Thomas H-o-oker. The Merrimack River has historically been important for transportation and industry, especially during the Industrial Revolution.