A 38 year old male suffered from redness and swelling of first meat-tarso phalangeal joint thrice over the past two years.He was found to be hypertensive and the EEG showed inverted 'T' waves in precordial leads. Which one of the following investigations will be diagnostic -

• A. Rheumatoid arthritis
• B. Serum uric acid
• C. E.S.R.
• D. Joint fluid aspiration