Final answer:
The sentence without a mixed construction is 'The Boston Tea Party occurred because protesters disagreed with the Tea Act of 1773.' because it clearly and grammatically correctly indicates the cause-and-effect relationship.
Step-by-step explanation:
The sentence that is not a mixed construction is: 'The Boston Tea Party occurred because protesters disagreed with the Tea Act of 1773.'
Here, we have a clear, straightforward sentence structure that explains the cause-and-effect relationship between two events without any grammatical confusion. Sentence structures in options a, c, and d are considered mixed constructions because they combine elements in a way that can be confusing or grammatically incorrect. Option a redundantly combines 'the reason' with 'because', option c improperly connects a clause with 'is why', and option d uses 'For protesters disagreeing' which is not standard English construction for expressing cause and effect.