The theme prominent is the death of a young man at the height of his strength and his career. Death of a young person is a common theme in poetry and this one is very famous because of the emotions that it awakens in a person. Poe was known for writing poems like this usually including young women who die before becoming old.
The answer is:
My mother is very tall but my father is even taller.
Conjunctions join clauses, words and phrases and they are usually used to avoid a sequence of short sentences. For example, <em>and, but, </em>and <em>or</em>.
In this case, the most suitable sentences to combine with a conjunction like "but" are the ones whose subjects are related (mother and father) and whose predicates have a similar structure: both describe height and one has a comparative form of the adjective tall, so they can be easily joined.
Grendel wages war, that is terrorizes Heorot and its inhabitants, because he is a carnivorous, devilish creature that is committed to disturbing the king's peace and prosperity of the realm. The Dragon, on the other hand, wages war simply because a slave stole a cup from the treasure he had guarded for ages. So, his motivation is retribution. Grendel is a subverted human, the descendant of Cain, so he challenges the king and his subjects. The Dragon is something less particular, a kind of irrational force that subverts the order itself. He strikes Beowulf's kingdom. The clash of the two of them will end with both being dead, and the conflict unresolved.
