Answer:
A)
Step-by-step explanation:
0.5 mm is 500micrometers
Just eyeballing the cell there is no way it could be B) or C).
In the circumstances of this question I think the only thing you can really do is look at the cell and try to make an approximate guess on the diameter. In a question like this it can be tricky with A) and D) being so close together in magnitude.
I think it is A). This is because it looks like it would take about 5 of the cell to reach the diameter of the microscope lens.
And 100micrometers is 1/5 of 0.5mm.