Which sentence in this introduction paragraph is most clearly the thesis statement?
(1) It's difficult to know when you should hold tight to your beliefs and
when you should let them go. (2) You may wonder whether you will
look weak if you change your mind. (3) In Sophocles's Greek tragedy
Antigone, the characters must decide whether to stick to their beliefs
or allow themselves to change. (4) By showing the audience what
happens to each character, Sophocles shows the dangers of being
stubborn.
A. Sentence 1
B. Sentence 4
C. Sentence 2
D. Sentence 3

sentences vary by structure as well as by function. there are compound, complex, and compound-complex sentences.

simple sentence

i like to read.

a simple sentence has one independent clause.

compound sentence

i like to read, and i also like to write.

a compound sentence includes more than one independent clause, connected by a coordinating conjunction (and, but, for, nor, or, so, or yet).

complex sentence

i prefer to read books that are bestsellers.

a complex sentence includes one independent clause and one or more dependent clauses. (a dependent clause is one that cannot stand alone.) types of dependent clauses include relative clauses (i kicked the boy who pinched me), adverb clauses (i am going home now because i have a curfew), and noun clauses (i don't know what to do next).

compound-complex sentence

although i prefer to read current bestsellers, i do like to read old agatha christie mysteries, and i also like some 20th-century science fiction.

compound-complex sentences take a bunch of clauses (multiple independent clauses, and one or more dependent clauses) and toss them together like a salad. although these sentences take practice to write in a grammatically correct fashion, they can hold a tremendous amount of meaning, and are common in academic writing.

ian mortimer in his book "the time traveller's guide to elizabethan england" uses a narrative in his style, which successfully conveys a clear description of the life in england in the 16th century. he writes in second person, which makes it comfortable to reader and easy to understand, he captures the readers attention with views of the landscape, the streets, the people including rich and poor. he also depicts some cultural traits from how people behave, eat or what they wear. his descriptions range from the social, economical, the political power to the examples of the life of common people. it could be tell that this book is about social history rather than a   novel.