"Find a web site that produces a large amount of data. Investigate caching by running fetchall twice in succession to see whether the reported time changes much. Do you get the same content each time? Modify fetchall to print its output to a file so it can be examined."
I was able to observe a faster response when requesting https://www.reddit.com twice in succession.
$ go run main.go https://www.reddit.com
2018-06-12 11:24:21.5074152 -0500 CDT m=+0.003000101
0.82s 331901 https://www.reddit.com
0.82s elapsed
$ go run main.go https://www.reddit.com
2018-06-12 11:24:24.5515894 -0500 CDT m=+0.004000301
0.20s 1064 https://www.reddit.com
0.20s elapsed