thirty days has september, april, june, and november is what type of device?\ninitialism\nacronym\npneumonic\…

Brief Explanations:

A mnemonic is a memory - aid device. The phrase "Thirty days has September, April, June, and November" helps people remember which months have 30 days. Initialisms are formed from the initial letters of words and pronounced as individual letters (e.g., FBI). Acronyms are also formed from initial letters but pronounced as a word (e.g., NASA). "Pneumonic" is an incorrect term here; the correct one for memory - aid is "mnemonic".

Answer:

D. mnemonic