Question

Select the appropriate synonym to complete the sentence. Try the exercise without using a dictionary, but if you have difficulty, you may use one. Remember that you want the word with the right flavor.
Unless he shows more prudence, his investments will _______ to nothing in a few months.
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Answer 1

Synonym means the same.  In other words, you can finish the sentence with multiple words that mean the same thing here.  Since I don't have the original word that was used, I can give you some different options.  One would be dwindle.  This means gradually diminish in size.  A synonym for dwindle would be decline or decrease, both of which would work here.  You could also use fade or wither.  

Answer 2

Unless he shows more prudence, his investments will fade to nothing in a few months.

That is what I can come up with. I hope it helps.