Identify the topic sentence:
People all over Britain worked to make, equip and support military, commercial and fishing fleets. So, many people found work in construction and maintenance work related to the shipping industry. Ships needed to be supplied with sails, ropes and other essentials; warships needed cannon and gunpowder; sailors and passengers needed food and these requirements kept people in employment throughout the year. Thus, seafaring was an important source of work for not only sailors and fishermen, but for many others.