Can you help Identify the sampling method used.

At the 1-mile marker of a marathon, a timekeeper shouts out the time elapsed to every 10th runner that passes by. A statistician records the times shouted.
A. convenience
B. voluntary response
C. random
D. systematic

A geologist visits 10 randomly selected lakes in the region and collects soil samples in randomly selected areas along each shoreline.
A. systematic
B. convenience
C. random
D. stratified

Both are random samples.