The correct answer is: C. T/A 1425.
A line clear ticket is a document that authorizes a train to proceed over a section of track. It is issued by a dispatcher or other authorized person after the track has been inspected and found to be safe for train movement. The ticket includes the train’s number, the direction of travel, and the section of track that is authorized for travel.
In this case, the train is traveling in the up direction, which means that it is traveling from the south to the north. The section of track that is authorized for travel is from milepost 1424 to milepost 1426. The line clear ticket number is T/A 1425.
The other options are incorrect because they do not match the information provided in the question. Option A, T/C 1425, is incorrect because the train is traveling in the up direction, not the down direction. Option B, T/D 1426, is incorrect because the section of track that is authorized for travel is from milepost 1424 to milepost 1426, not from milepost 1425 to milepost 1427. Option D, T/B 1425, is incorrect because the line clear ticket number is T/A 1425, not T/B 1425.