Two identical spheres move in opposite directions with speeds `v_(1)` and `v_(2)` and pass behind an opaque screen, where they may either cross without touching (Even 1) or make an elastic hand-on collision (Event 2).
A. We can never make out which event has occurred
B. We cannot make out which event has occurred only if `v_(1) = v_(2)`
C. We can always make out which event has occurred
D. We can make out which event has occurred only if `v_(1) = v_(2)`
