Must let the vehicle go within one lane + change lanes where permitted + signal.
Answer 1 is incorrect because let the vehicle go in any lane which way. Answer 3 is incorrect because of the lack of change lanes where allowed.
Let the vehicle go in any lane; when it is necessary to change lanes, the driver must have a warning light and must ensure safety.
Vehicles must be kept in one lane and only allowed to change lanes where allowed; when changing lanes, there must be a warning signal and must ensure safety.
Vehicles must be driven in one lane, when changing lanes, there must be a warning signal, pay attention to ensure safety.