B is the correct answer.

A is wrong because of the use of since and wordiness.Since can be used either to mention a time frame or used instead of because.Here the usage can be interpreted in both ways making this option to have a two different meaning in each case.Eliminated because of a change in the intended meaning

B is Correct because it uses because instead of since thus establishing a Causation and also uses a participle modifier (Expecting) to imply a simultaneous action.This choice is best among the all.

C is Wrong because of the use of are expecting -a present continious tense- as i found that to be inapropriate in this context.

D is Wrong because of the placement of modifier "Written by Senator Johnston".At its current placement,It mean the estae tax code is written by the Senator Johnston but according to the intended meaning only revision of the estae tax code is done by Senator Johnston.

E is Wrong because of the use of "which" to modify an action,Which can only be used to modify noun and never can modify a clause.Here we need a clause modifier instead of a Which to correctly modify the previous dependent clause.

Correct me if i am wrong.

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