Consider the following specifications of gears A, B, C and D.
| Gears |
A |
B |
C |
D |
| Number of teeth |
20 |
60 |
20 |
60 |
| Pressure angle |
14$\frac{1}{2}$0 |
14$\frac{1}{2}$0 |
200 |
14$\frac{1}{2}$0 |
| Module |
1 |
3 |
3 |
1 |
| Material |
Steel |
Brass |
Steel |
Brass |
Which of these gears from the pair of spur gears to achieve a gear ratio of 3?
(a) A and B (b) A and D (c) B and C (d) C and D