Fuel containers shall be ____________ to prevent jarring loose.

The correct response emphasizes the importance of ensuring safety and stability for fuel containers during any activity involving them. When fuel containers are mounted, they are affixed in a manner that prevents them from moving or shifting, which is crucial in preventing spills, leaks, or accidents due to the containers jarring loose. Proper mounting creates a secure hold, which is particularly important given the volatile nature of the contents within these containers.

The other options, while related to the handling of fuel containers, do not convey the same level of safety and control. Storing containers may imply they are placed in a designated area, but without adequate measures for preventing movement, they could still become a hazard. Transporting suggests movement from one location to another, which involves risks if the containers are not secured properly during transportation. Though securing might seem like a close option, in the context of mounting, it does not convey the installation aspect that implies a more permanent solution against movement. Hence, mounting is the most accurate choice for preventing fuel containers from becoming loose.