The correct answer is C. have been teaching.
The sentence is in the present perfect continuous tense, which is used to talk about an action that started in the past and continues to the present. In this case, the speaker has been teaching English online since July 2014, and they are still teaching English online now.
The other options are incorrect because they do not accurately reflect the meaning of the sentence. Option A, am teaching, is in the present tense, which would be used to talk about an action that is happening right now. Option B, have taught, is in the simple past tense, which would be used to talk about an action that happened at a specific point in time in the past. Option D, teaching, is the gerund form of the verb “teach,” which would be used as a noun or as a modifier.
Here are some examples of how the present perfect continuous tense can be used:
- I have been working here for 5 years.
- She has been waiting for you for an hour.
- We have been playing soccer since we were kids.
- They have been studying for the test all night.