Correct option is D
The correct substitution of the highlighted words is (d)
for two hours.
Explanation: Use
for with a
period/duration (
for two hours, for three days), and
since with a
point in time (
since 5 p.m., since Monday). The sentence talks about a
duration, so
for two hours is correct. You can write:
“We waited for him for two hours.” (Stylistically, to avoid double
for, you can also say
“We waited two hours for him.”)
Grammatical rule used:
·
for + period (duration):
for two hours, for a week.
·
since + point (starting time):
since 6 o’clock, since January.
·
Example:
She has been studying
for
three hours. /
She has been studying
since
6 a.m.
Information booster:
Since frequently pairs with
perfect (continuous) aspects:
I have waited since noon. But
“since two hours” is wrong because
two hours is a duration, not a starting point.