Which example needs a transition word or phrase between sentences to connect the ideas?

A$.)$

Engaging your employees in a day of service is a good way to make a difference in your community. The costs associated with shutting down your business for a full day may be significant.

B$.)$

Many students don't clearly understand what constitutes plagiarism. Therefore, plagiarism is often unintentional.

C$.)$

Real estate sales have moved in tandem with the stock market for the last $15$ years. When the stock market has expanded, real estate sales have increased.

D$.)$

Several significant hurricanes have hit the region in recent years. The damage done by them has caused insurance rates to rise.