The correct answer is A. futile.
A futile action is one that is pointless or useless. In this case, the person is taking casual leave quite often, which means that they are not using their leave time for its intended purpose. This could be because they are not feeling well, or because they have other personal commitments that they need to attend to. However, it is also possible that they are taking leave simply because they do not want to work. Whatever the reason, taking casual leave too often can be seen as a sign of irresponsibility or laziness.
The other options are not correct because they do not accurately describe the person’s behavior. A regular action is one that is done on a regular basis. In this case, the person is not taking leave on a regular basis, but rather quite often. A formal action is one that is done in a formal manner. In this case, the person is not taking leave in a formal manner, but rather in a casual manner. A systematic action is one that is done in a systematic manner. In this case, the person is not taking leave in a systematic manner, but rather in a haphazard manner.