$P, Q, R,$ and $S$ crossed a lake in a boat that can hold a maximum of two persons, with only one set of oars. The following additional facts are available.

1. The boat held two persons on each of the three forward trips across the lake and one person on each of the two return trips.
2. $P$ is unable to row when someone else is in the boat.
3. $Q$ is unable to row with anyone else except $R.$
4. Each person rowed for at least one trip.
5. Only one person can row during a trip.

Who rowed twice?

1.  $P$
2. $Q$
3. $R$
4. $S$

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By going through the above criterion we can conclude the following statements

In the first forward trip, Q and R will go and on this trip, Q will row.

Now, R will come back on the 1st return trip and R will row.

In the 2nd forward trip, R and P will go and R will row.

Now, P will come back on the 2nd return trip and P will row.

In the 3rd forward trip, P and S will go and S will row.

So, R rowed Twice. option C)

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