A student puts together the apparatus shown in the diagram in order to determine the centre of mass of the card. The student checks that the card, the string and the bob are all stationary. What should the student do next?
- AMark a horizontal line on the card level with the middle of the string.
- BMark the line of the string on the card.
- CPull the bob on the string to one side and release it.
- DReplace the bob with a heavier bob.