The correct option is
A Though
Option B - 'As' is used to explain reasons in a sentence. For example, 'I can't come to school as I am sick.' As the given sentence doesn't any reason, we can't use 'as' here. Thus option B is incorrect.
Option C - 'Since' is used to explain the duration of an action that started at a particular time and hasn't ended yet. For example, 'I have been working since 2010.' As the given sentence doesn't explain the duration of the action, we can't use 'since' here. Thus option C is incorrect.
Option D - 'For' is used to explain the duration of an action that started and ended at a particular time. For example, 'I worked there for five years.' As the given sentence doesn't explain the duration of the action, we can't use 'for' here. Thus option D is incorrect.
Option A - 'Though' means 'despite'. For example, 'Though I was sick, I went to work.' As the given sentence explains a situation that happens despite the other situation, we can use 'though' here. Thus option A is the correct answer.
'Though he gets up late, he reaches school on time.'