1.
When he
P : did not know
Q : he was nervous and
R : heard the hue and cry at midnight
S : what to do

The Proper sequence should be:

2.
It has been established that
P : Einstein was
Q : although a great scientist
R : weak in arithmetic
S : right from his school days

The Proper sequence should be:

3.
Then
P : it struck me
Q : of course
R : suitable it was
S : how eminently

The Proper sequence should be:

4.
I read an advertisement that said
P : posh, air-conditioned
Q : gentleman of taste
R : are available for
S : fully furnished rooms

The Proper sequence should be:

5.
Since the beginning of history
P : have managed to catch
Q : the Eskimos and Red Indians
R : by a very difficulty method
S : a few specimens of this aquatic animal

The Proper sequence should be: