word choice - What are the differences between "disseminate", "propagate" and "spread"?

What are the differences between the three words: disseminate, propagate and spread?

Here are some examples from a fill-in-the-blank test:

1. News is __ by means of television and radio. (disseminated)



2. Don't __ malicious reports. (propagate)


3. Some people are keen on __ rumours. (spreading)

I want to know the specific differences of the three words, and why they cannot be replaced with each other.