The correct option is A land, sea
The first Persian attack on Greece failed due to contraction of diseases and lack of food. It did not even reach Greece, but had to go back. In the second invasion in 490 BC., they avoided the land route and came by sea route, landing at a place called Marathon near Athens. Hence, Option A is correct. Among the rest, B implies that the Persians came by land, but that was in first invasion. Air invasion was not possible as aircrafts were invented much later in nineteenth century. Hence, these are incorrect.