Critical Reasoning

Criminals released from prison on parole have generally been put under routine supervision. A recent program has allowed criminals to leave prison early under intensive supervision; they must obey curfews and in some cases they must be electronically monitored. The percentage of released criminals arrested while under supervision is the same for intensive supervision as for routine supervision, so intensive supervision is no more effective than routine supervision in preventing criminals from committing additional crimes.

Which one of the following is an assumption on which the argument relies?

(A) The criminals under intensive supervision, but not those under routine supervision, were required to work or attend school during their supervision period.
(B) All of the criminals who were arrested while under routine supervision had been in prison more than once before being paroled and put under supervision.
(C) The proportion of arrests to crimes committed was not significantly higher for criminals under intensive supervision than those under routine supervision.
(D) Of the criminals arrested while under intensive supervision, some would not have committed crimes if they had been under routine supervision.
(E) The number of criminals put under routine supervision was not significantly greater than the number of criminals put under intensive supervision.

What's the best approach to determine the answer? Can any experts help?

How do we find assumptions? There are many ways, but the first step is to identify the conclusion of an argument. In this case the conclusion is:

Intensive supervision is no more effective than routine supervision in preventing criminals from committing additional crimes.

Why? Why does the argument think so? Because:

The percentage of released criminals arrested while under supervision is the same for intensive supervision as for routine supervision.

What's the assumption? Well, one way to find an assumption is to look for new, surprising words in the conclusion-words or concepts that are not mentioned in the premises. In this case, the conclusion is about COMMITTING CRIMES whereas the premise talks about BEING ARRESTED. Are these two concepts the same? Isn't it possible that someone could be arrested without having committed a crime or that a person might commit a crime yet not get arrested for it? Perhaps those under intensive supervision are invariably caught every time they commit a crime whereas those under routine supervision are caught no more than once every 3 or 4 crimes committed.

(C) is the answer that fits in well with the reasoning we have already explored above.