The text argues that since the incidence of schizophrenia has remained stable and the use of cannabis has increased, it cannot be true that smoking cannabis causes schizophrenia. This is effectively saying that cannabis does not cause schizophrenia.
We need to find a weakness in this conclusion.
A – Wrong
This actually supports the argument as it says that cannabis does not cause schizophrenia.
B – Wrong
Cancer is not related to the argument.
C – Wrong
This is irrelevant to the argument as it does not mention either cannabis or schizophrenia.
D – Wrong
Tar and tobacco is irrelevant to the argument.
E – Correct
If under 15 year olds have only recently started smoking, then we would have to wait for some time to see the correlation between cannabis and schizophrenia.