Statistics question homework

I was given this question by a friend that he got on a test? Does anyone know the answer?

A case control study of risk factors for testicle cancer identified heavy smoking, as one of the major risk factors. And can you explain why, I've been tearing my hair on this one...

Results:

----------Heavy_smoker
----------|No--| Yes |----Total
Cancer---+----------------------+----------
No------| 650 | 105 |---755
Yes------|100 | 90 |----190
-----------+----------------------+----------
Total-----|750--| 195 |-- 945

Row and column probabilities can be calculated for table above, but only one of these alternatives is meaningful. Which and why?