2. Prepositions
can
work
as
connectors between words in a
sentence. By using “in” , “at ”, or
“on”, we can describe when the
thing occurs.

3.  We use at
for
specific times.
 We us on for
specific dates and
days. We also use
on for some special
days.
 We use in for
nonspecific
times
during a day, a
month, a season or
a year.

4. 
[Today it is possible to be productive, keep in constant contact with
associates, and have fun at the same time.]
•
[The race begins in death valley, california at an elevation285feet below
sea level, in July, the hottest month of the summer.]
•
[However recearch shows that few people can truly function well on
less than eight hours' sleep per night.]
Pp. 25