A - Incorrect: It does not make sense for the second pronoun it to refer to the same entity that the first pronoun it refers to. It is also unclear what the second pronoun refers to.

C, D - Incorrect: It is not clear what the pronoun that refers to. Its usage here is also colloquial and unidiomatic.

E - Incorrect: The meaning of the original sentence has changed: The use of unusual is not the same as not usual. The infinitive to do is missing an object.

B - Correct: The use of to do so clearly conveys the intended meaning of the sentence.
The correct answer is B