In the text,

the relative pronoun “that” (l.1) can be correctly replaced by which.

In the text,

the article “a”, in “a circle” (l.2), can be correctly replaced by the.

In the text,

the function word “as” (l.10) can be correctly replaced by like.

In the text,

the phrase “They can be used as warmers” (l.12) is the passive voice of You can use them as warmers.

In the text,

the word “filler” (l.13) is a noun formed from the verb to fill.

In the text,

the phrase “at the end” (l.13) is synonymous with in the end.

In the text,

the use of “will”, in “each student will have” (l.32), shows agreement.

In the text,

the relative pronouns which and that can be used after the word “topic” (l.43) without changing the meaning of the sentence.

In the text,

“thinking” (l.45) is in the -ing form because it comes after a preposition.

In the text,

the verb “Beware” (l.45) implies a warning.