The diagram shows a graduated slide, with divisions of 0.1 mm viewed using an eyepiece graticule. 0 10 20 30 40 50 60 70 80 90 100 Pollen grains were grown in a sugar solution and viewed using the eyepiece graticule. Diagram 1 shows the pollen grains at the start. Diagram 2 shows the pollen grains after four hours. 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 at start after 4 hours diagram 1 diagram 2 pollen tube What is the growth rate of the pollen tubes? A 5µmh–1 B 10µmh–1 C 5 mmh–1 D 10 mmh–1