The correct option is
D Employees whose commutes are shortened will use the time saved to do additional productive work for their employers
Option B is the correct answer because details in the second paragraph strongly suggest that researchers (“we”) at the Martin Prosperity Institute assume that shorter commutes will lead to more productive time for workers. Those at the institute “calculate that every minute shaved off America’s commuting time is worth $19.5 billion in value added to the economy”, it can reasonably be concluded that some of that added value is from heightened worker productivity.
Option A is incorrect because there is no evidence in the passage that researchers at the Martin Prosperity Institute assume that employees who work from home are more valuable to their employers than employees who commute. Although the passage does criticize long commutes, it does not propose working from home as a solution.
Option C is incorrect because there is no evidence in the passage that researchers at the Martin Prosperity Institute assume that employees can conduct business activities, such as composing memos or joining conference calls, while commuting.
Option D is incorrect because there is no evidence in the passage that researchers at the Martin Prosperity Institute assume that employees who have lengthy commutes tend to make more money than employees who have shorter commutes. The passage does not draw any clear links between the amount of money employees make and the commutes they have.