The correct answer is C. am doing.
The sentence “Don’t disturb me. I am doing my homework” is in the present continuous tense. This tense is used to talk about actions that are happening at the moment of speaking. In this case, the speaker is asking the listener not to disturb them because they are currently doing their homework.
The other options are incorrect because they do not express the action as being ongoing. Option A, “do,” is in the simple present tense, which is used to talk about general truths or habits. Option B, “doing,” is the present participle, which is used to form the present continuous tense. Option D, “was doing,” is the past progressive tense, which is used to talk about actions that were happening at a specific time in the past.
In conclusion, the correct answer is C. am doing.