The correct answer is: C. Is what I mean understood by you?
The other options are incorrect because they use the past tense or the present perfect tense, which are not appropriate for this situation. The speaker is asking for confirmation that the listener understands what they are saying, so the present tense is the most appropriate tense to use.
Option A: “What I mean is that understood by you?” is incorrect because it uses the past tense. The speaker is not asking about something that happened in the past, they are asking about something that is happening right now.
Option B: “Was what I mean understood by you?” is incorrect because it uses the past perfect tense. The speaker is not asking about something that happened before a specific time in the past, they are asking about something that is happening right now.
Option D: “What I mean is understood by you?” is incorrect because it uses the present tense, but it is not a question. The speaker is not asking for confirmation that the listener understands what they are saying, they are simply stating that the listener understands what they are saying.
Therefore, the correct answer is: C. Is what I mean understood by you?