You can either choose one option, or multiple options:
If you choose one option, you will score 1 if it is the correct option, and zero otherwise.
If you choose more than one options, and if the correct option is among your chosen options, you will receive a fractional score, 1 divided by the number of chosen options, and zero otherwise.
For example, suppose Option 5 is the correct answer,
If you choose Option 5 as your answer, you will receive 1 score.
If you choose Options 1, 5, 7 and 8, since Option 5 is among the options you choose, and you choose four options, you will score 1 divided by 4, which is 0.25.