An eyepiece lens in a microscope may be fitted with an eyepiece graticule. Which of the following statements about eyepiece graticules are correct? 1. They determine the true length of cells in micrometres. 2. They allow biologists to draw cells in the correct proportions. 3. Their size changes when the objective lens is switched from $\times 10$ to $\times 40$.
- A1, 2 and 3
- B1 and 3 only
- C1 only
- D2 only