Answer:
Every time they are dirty.
Explanation:
If you don't change the towels out for the sandwich station every time they get dirty, it can lead to some food born illnesses that you can potentially give customers. If a customer gets a FBI, you can lose a customer, or get sued. It is always best to change them every time they are visibly dirty to prevent accidents like FBIs from happening.
A personal story or example
The correct answer is the first option.
The sentence that presents the correct subject-verb agreement is the first one since in it we are talking about "heavy rains" OR "fast-melting snow". In other words, the subject is coordinated by the conjunction "OR" which makes the subject singular. The verb "causes" is conjugated in the third person singular.
<span>Words of the same root with different affixes are well
thought-out different words, so in that regard it would follow that there would
be more words. But if you mean there might be a capability to change an
existing word simply and clearly put off or negate people inventing entirely
new words, root and all? In that circumstance, especially considering each
modification of a root is in theory a separate word, there would be no much
impact; all words have to start from somewhere.</span>
