Over the centuries the story has been told and retold and told again, often with a widely varying cast of characters. knights, priests and priestesses, kings and queens, and various users of magic come and go, but always there is arthur, the sun around which all else revolves, his faithless wife (guinevere), his equally-faithless best friend (lancelot), the illegitimate son (mordred) who becomes his bane—and merlin. whatever his role, merlin is always there, and it is always clear that arthur could not have existed, survived, or become king without him.

martians or other types of aliens represent a unique fear as opposed to zombies. vampires and other types of monsters.   in most sci-fi stories, aliens come from other worlds and have different or more advanced technology.   abductions and experimentation on human bodies that involve these technologies, or the use of these technologies against human beings and the use of unknown "powers", are a type of fear that's different from that of other types of monsters.  

in other words

to put it differently

for one thing

as an illustration

in this case

for this reason

to put it another way

that is to say

with attention to

by all means

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another key point

first thing to remember

most compelling evidence

must be remembered

point often overlooked

to point out

on the positive side

on the negative side

with this in mind

notably

including

like

to be sure

namely

chiefly

truly

indeed

certainly

surely

markedly

such as

especially

explicitly

specifically

expressly

surprisingly

frequently

significantly

particularly

in fact

in general

in particular

in detail

for example

for instance

to demonstrate

to emphasize

to repeat

to clarify

to explain

to enumerate