The correct answer is: C. has been flying
The sentence “He has been flying an airplane for 10 hours” is in the present perfect continuous tense. This tense is used to talk about an action that started in the past and is still happening now. In this case, the action is “flying an airplane”. The sentence tells us that the person has been flying an airplane for 10 hours, and is still flying.
The other options are incorrect because they do not accurately describe the action that is happening in the sentence. Option A, “has flown”, is in the simple past tense. This tense is used to talk about an action that happened at a specific time in the past. In this case, the sentence would mean that the person flew an airplane at some point in the past, but is not flying now. Option B, “is flying”, is in the present tense. This tense is used to talk about an action that is happening right now. In this case, the sentence would mean that the person is flying an airplane at this very moment. Option D, “will fly”, is in the future tense. This tense is used to talk about an action that will happen in the future. In this case, the sentence would mean that the person will fly an airplane at some point in the future.
I hope this explanation is helpful!