Table R (A) contains records {1,2,3}. The following movements are simultaneously they are working.

T1: "update R set A = 2 * A; COMMIT;"

T2: "select SUM (A) from R; COMMIT;"

T3: "select SUM (A) as c from R; select AVG (A) as a from R; COMMIT; "

a) T1 can be graded; If T2 is in "read uncommitted" isolation; What values can T2 end with?

b) T1 can be graded; If T3 is "read committed" insulation; What binary values (c, a) can T3 end with?