Answer: C. 70 percent
Explanation:
Given, Time for the first unit = 50 minutes
Time for the second unit = 35 minutes
The unit improvement factor learning curve = (The time for the second unit) ÷ (time for the first unit) x 100.
So, The unit improvement factor learning curve = 35÷ 50 × 100 = 70 percent.
Hence, the correct option is "C. 70 percent".