Heart that fed: And on the pedestal these words appear: 'My name is Ozymandias, king of kings: Look on my works, ye Mighty, and despair!' Nothing beside remains. Round the decay Of that colossal wreck, boundless and bare The lone and level sands stretch far away.
I think the questions that must be ask are:
a.What does “encryption” mean?
d.What are “key distribution problems”?
All the text is based on the concept "encryption" so it is very important to know what it means in order to undestand the rest of the information. If not, you will be missing important facts. In addition, there are a lot of words used that are derived from this one, so you won't be able to undestand them.
Another important concept that gives a lot of information just by knowing it's meaning is "key distribution problems", they could be two or a thousand, it is important to know what they are and what they do.
The other question that seems important is the one of the "public key cryphtography" but this one can be inferred by the context.
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D) Verb: has been raining Mood: indicative
The entire verb phrase is "has been raining". "Has" and "been" are both helping verbs that create the present progressive tense. This tense is used to show something that is happening and has been happening for a period of time. The indicative mood is correct because the indicative mood indicates something that fact. Interrogative mood is question form. Conditional form is based on something else happening.