The answer is D. <em>While </em>and <em>however</em>.
A doesn't work because "both" is a word of comparison, B isn't right because "also" is a transitional word and has nothing to do with contrasting the two animals, and C is incorrect because "similar" isn't a word of contrast; instead, it's a word you use when you compare two things.
Hope this helps!
The overriding idea in any piece of fiction is known as its theme.
We could add a solar heating to the greenhouse, or we could build a rainwater collection system for the same cost.
