C
Researcher: Overhearing only one side of a cell-phone conversation diverts listeners' attention from whatever they are doing. Hearing only part of a conversation leaves listeners constantly trying to guess what the unheard talker has just said. Listeners' attention is also diverted because cell-phone talkers speak abnormally loudly. The researcher's statements, if true, most strongly support which one of the following?
A: The risk that a driver will cause an accident is increased when the driver is talking on a cell phone.
B: People who overhear one side of a cell-phone conversation inevitably lose track of their thoughts.
C: When a driver hears a passenger in the driver 's vehicle talking on a cell phone, that detracts from the driver 's performance .
D: Conversing on a cell phone requires making more guesses about what one's conversational partner means than other forms of conversation do.