If the driver does not received all right signal from the guard, he must call for is by giving. A. Two sharp whistles B. One long one short. C. On long D. None of these

The correct answer is A. Two sharp whistles.

The driver must give two sharp whistles if he does not receive the all-right signal from the guard. This is to alert the guard that there is a problem and that the train should not proceed.

Option B is incorrect because one long whistle is the signal to proceed. Option C is incorrect because one long whistle is the signal to stop. Option D is incorrect because it is not a valid option.