What are some reference words?

In the words of…
As noted by…
Per…
The Institute of Apples, a recognized authority on the topic, says…
Leading apple-ologists agree with…

Or you could always do what I do: This reminds me…

You could footnote the reference. “The incidence of death from breast cancer fell between 1970 and 2000 fell from 56.3% to 20.5% (1)

(1) American Cancer Society, 2008

xxx yyy zzz here stands for an attributable statement.

   In a 2008 report, the ACS states that xxx yyy zzz.

   Findings of a study by the ACS (2008) show that xxx yyy zzz.

   Researchers for the ACS (2008) have found that xxx yyy zzz.

And variants on those constructions. Or just state it and attribute it:

   Xxx yyy zzz (ACS, 2008).

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By the way, @Aesthetic_Mess, I’m one of the sticklers on homework questions, and I don’t consider this to be out of bounds at all. You’re asking for genuine help with your task and not for someone else to do the work in your place. Nothing wrong with that, in my opinion, and no reason to be shy about it.

So-and-so suggests that…
As maintained by So-and-so, ...
So-and-so writes: ...

Sorry for the badly worded sentence. Talking and typing is impossible these days.

Those are called signal phrases.

Here’s a pretty good list of them.

You will find in this manual entitled XYZ that…

Some good information about apples can be found in this article XYZ.

When looking for well researched information about apples the XYZ’s website can offer a lot of suggestions.

The XYZ website shows that apples…

A few different books, including ABC and XYZ have complete information about apples.

@Everyone Thank you guys! This helped a bunch