These are not line plots; they are dot plots. Each dot (×) represents one data point. The dot is placed above the corresponding value on the horizontal axis. There are 7 data points, so should be 7 dots. 3 of the data points are 3/4 hour.
Only plots C and D show 7 data points. Only plot C shows three of those data values being 3/4 hour. Plot C is the correct choice.
