This is a simple sentence because in its entirety it is a single clause. There are no multiple independent clauses connected or any subordinate clauses to make it compound or complex.
Answer:
Aphorism
Explanation:
Anagram is a word, phrase, or name formed by rearranging the letters of another. I don't think this is it because they is no words that were rearranged.
Aphorism is a pithy observation that contains a general truth. This could be true!
Analogy is a comparison between two things. This is not it because there are not two things being compared.
Allusion is an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference. This is not it because this sentence is explicit meaning it is very straight foward.
Out of all four of those... I would go with Aphorism.
The correct answer is a Dictionary.
A thematic statement is one or more complete sentences that express a theme. They can also be called or considered a thesis.
Answer:
It is preferable to study English in an English speaking country
