What was the maximum surface speed of the early British E-class submarines, such as HMS E7?

A. 20 knots (37 km/h; 23 mph)
B. 16 knots (30 km/h; 18 mph)
C. 10 knots (19 km/h; 12 mph)
D. 12 knots (22 km/h; 14 mph)
Answer: 