Something that may be of use to you, that would be of good support to Language Change over Time, would be to look at two texts, one foreign, and one English, and compare the origins of the different word classes.
I.e lots of concrete nouns came from the Nordics, back when everyone was staking their claim on England. French may be good, as that was the official language of England for a while back in something like the 15th century.
These would have had an influence on the language we use today, and you could compare how the modern European languages stemmed from the old languages such as Latin, Greek, and the surrounding islands.
You could extend it to show how when people were able to travel much more (so maybe old texts and new texts) how words from many more languages came in as people were travelling around the world.
That's just my idea of what I'd do now I have finished the course :L
My investigation was into the language choices of female leads in video games and other media. It was alright, but I like the idea I just came up with a lot more :L
Good Luck, it is a long and arduous task that my class hated, a lot!