Multiple Choice - Which one represents linear regression

Which of the scenarios below is most appropriate for simple linear regression.

Im not sure, but isnt an assumption of linear reg, that the two vairables are independent. yet for some reason i think the answer is A. can i get some help?

http://webct.anu.edu.au/web-ct/en8/img/shim.gif

a. An investigation is carried out to determine whether number of hours of study is related to the final mark (as a percentage) in a first year economics course. b. I wish to predict the future earnings of a student based on whether they are left or right handed. c. Data is collected for the purpose of determining if eye colour is related to choice of coffee or tea. d. You aim to investigate the relationship between the number of assignments due per week and whether the week contains a public holiday (yes or no).