Hey HaeWon!

Oh, I'm so sorry if I pointed to the 7.4% saturation line (the solid line)! I was supposed to refer to the dry sand, which is the line just below the solid line.

I know the lines are a bit hard to read and see (I'll make sure to change that next time =)), so in case you aren't sure about which lines refer to which percentage of saturation, here they are. The highest line is the solid line - 7.4% saturation. Below that is the dry sand (0% saturation). Below the dry sand is 1.5% saturation. Lastly, the lowest line is the 5% saturation.

So, if the dry sand line is the line we are looking at for answer choice C, then the greatest force is between 5 and 6 (about 5.5 mm). This would still make answer choice C incorrect since the force is greater than 5 mm.

Sorry about the hard-to-read lines, and thank you for your wonderful question. I'll make sure to be clearer and more accurate with my explanations.

Keep Moving Forward!