Final answer:
To avoid background radiation artifacts when using CR, it is important to erase image plates if there is any question about the time since they were last erased, especially in pediatric radiography.
Step-by-step explanation:
In order to avoid background radiation artifacts when using CR, it is important to erase all image plates if there is any question about how long it has been since the plate has been erased (option B). Erasing the plates ensures that any residual radiation from previous exposures is removed, reducing the risk of artifacts in subsequent images. This is particularly crucial in pediatric radiography where minimizing radiation dose is important (option C). Therefore, the correct actions to avoid background radiation artifacts when using CR are options B and C, making the answer E.