Correct Response: B. Chlorofluorocarbons (CFCs) developed for air conditioning systems eventually became concentrated enough in the atmosphere to reduce the extent and concentration of the stratospheric ozone layer. This layer of ozone protects life from harmful solar radiation. The threat was so serious that nations acted to ban chlorofluorocarbons. Radioactive isotopes used in medicine (A), while potentially dangerous, have been widely hailed as being an important tool for doctors and their use is not seen as having unintended consequences. Lithium-ion batteries are considered safer for the environment and people than other types of batteries that typically contain toxic metals, such as lead or cadmium (C). The use of electromagnetic waves for transmission of data (D) has produced no serious unintended consequences for human health.
