Consider a database table ‘Knowledge’ with attributes a1, a2 and a3. Which of…

1. A.

   SELECT a1, a2,a3 , COUNT(*) FROM Knowledge GROUP BY a1, a2, a3;

2. B.

   SELECT a1 FROM Knowledge;

3. C.

   SELECT a1, COUNT(*) FROM Knowledge GROUP BY a1;

4. D.

   SELECT a1, COUNT(*) FROM Knowledge;

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