A. Over a billion people using MicrosoftWindows operating systems
B. Over a billion people uses Microsoft Windows operating systems
C. Over a billion people use Microsoft Windows operating systems
D. Over a billion peoples use Microsoft Windows operating systems
Explanation: Option (a) sentence structure ঠিক নেই, Option (b) 'people' plural হওয়ায় singular verb 'uses' বসবে না, Option (d) 'people' এর সাথে-s বসে না। তাই সঠিক answer option (c).
