Final answer:
The correct answer is option c) generally are used when freight is carried part way by rail or ship, as containerized loads facilitate intermodal transportation. They are not exempt from hazardous materials regulations and are used for various types of cargo, not limited to perishable goods.
Step-by-step explanation:
Containerized loads are a pivotal element of modern transportation, and their use has dramatically changed the shipping and manufacturing landscapes. The correct answer to the question of why containerized loads are generally used is option c) generally are used when freight is carried part way by rail or ship. This method of shipping allows for intermodal transportation, which is the process where cargo can be transported by multiple transportation modes like trucks, trains, and ships without direct handling of the freight itself when changing modes.
Containers are not exempt from hazardous materials regulations; regulations such as those by the United States Department of Transportation and EPA's hazardous waste regulations still apply to containerized loads. This eliminates option a) as being correct. They are also not exempt from weight limit restrictions, dismissing option b). Moreover, option d) is inaccurate because containers are used for a wide range of goods, not just perishable ones.
This is proven by the versatility and efficiency containerization has brought to the shipping industry, making it cost-effective for a wide range of cargo, as opposed to solely perishable goods.