K	P	G
1	0	red
2	NULL	red
3	0	blue
4	9	red
5	NULL	blue

Table T has 5 rows of 3 columns of data as shown above, where NULL means no data. The query below

SELECT AVG(distinct P) FROM T WHERE P IS NULL;

should return

a.)0

b.)3

c.)4.5

d.)NULL