Eighty-year-old martha knows her memory is not what it used to be, so when she decides something is really important to remember she makes up a rhyme about it. martha is using a(n):

The correct answer is a mnenomic device.

A mnemonic device refers to a memory technique in order to encode,retrieve and recall some information on future occasions. Mnemonic devices can be rhymes, phrases or acronyms that are used to combine and remember two or more unrelated or distinct concepts. They are useful for remembering lists, confusing information or large chunks of information. 

That is true , instead try to have a sit down talk with them