4. Keep your mobile phone .... at night. A. fitted B. switched on C. switched off

Translation of the instruction: Обведите правильный ответ.

Answer: Keep your mobile phone switched off at night. (На ночь выключай мобильный телефон.)

Explanation: Switched off means not operating; it fits the advice about nighttime. (Switched off означает «выключенный» и подходит к совету о ночном времени.)