______ml + _______ml + = 3l.

The correct answer is: 1.5l, 1.5l

GIVEN-
______ml + _______ml + = 3l
TO FIND-
Missing values
SOLUTION-
a. 1.5l, 2.5l
1.5l = 1.5 * 1,000 ml = 1,500 ml ................................. (1l = 1,000 ml)
2.5l = 2.5 * 1,000 ml = 2,500 ml ................................. (1l = 1,000 ml)
3l = 3 * 1,000 ml = 3,000 ml ................................. (1l = 1,000 ml)
 ______ml + _______ml + = 3l
∴        1,500 ml + 2,500 ml = 3,000 ml
∴                          4,000 ml ≠ 3,000 ml
Since LHS ≠ RHS, Option A is incorrect.
b. 1.5l, 1.5l
1.5l = 1.5 * 1,000 ml = 1,500 ml ................................. (1l = 1,000 ml)
3l = 3 * 1,000 ml = 3,000 ml ................................. (1l = 1,000 ml)
 ______ml + _______ml + = 3l
∴        1,500 ml + 1,500 ml = 3,000 ml
∴                          3,000 ml = 3,000 ml
Since LHS = RHS, Option B is the correct answer.
Final Answer:-
Option 'b'  is the correct answer to the given question.

Since we got the correct answer at option b, there is no need to solve for further options c & d.