Use evidence from the fact that a ruler is used for measuring the length of an object to answer the following question. Choose from options. "Harriet wants to know the area of a rectangular sheet of paper. Its size is unknown to her. Which one of these will be the only tool that she needs?"

OPTIONS:
[i] a ruler.
[ii] a compass.
[iii] a calculator.
[iv] a protractor.
[i]