<>"When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. If you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term."<>
D. All laborers can now get a good investment plan.
A good way of judging active voice is to see what is the most concise, simple way of stating a sentence. "Could now" "will now" and "would now" seems a bit awkward, therefore D is the correct answer.