Answer:
The plural form of "bank deposit" is "bank deposits".
Step-by-step explanation:
In the English language, the most common way to change a word from singular to plural is by adding an -s to its end. There are, of course, some exceptions such as "woman" and "women" but, in general, adding -s will suffice.
The plural form of "bank" is "banks", and of "deposit" is "deposits". Why then the plural of "bank deposit" is not "banks deposits"? The word "bank" is accompanying the word "deposit", giving it an attribute, a quality - it's not just a deposit, it's a bank deposit. That's what adjectives do, and adjectives should not change their form into plural - beautiful girl, but not beautifuls girls. Thus, because "bank" is functioning as an adjective in the structure "bank deposit", it does not change. In conclusion, the plural form of "bank deposit" is indeed "bank deposits".