If you think of the equation as an equation for a line. =+
y
=
m
x
+
b

where

=5/9(−32)
C
=
5
/
9
(
F
−
32
)

or

=5/9−5/9(32)
C
=
5
/
9
F
−
5
/
9
(
32
)

you can see the slope of the graph is 5/9
5
/
9
, which means that for an increase of 1 degree Fahrenheit, the increase is 5/9
5
/
9
of 1 degree Celsius. Therefore, statement I is true.

This is the equivalent to saying that an increase of 1 degree Celsius is equal to an increase of 9/5
9
/
5
degrees Fahrenheit. Since 95
9
5
= 1.8, statement II is true.

On the other hand, statement III is not true, since a temperature increase of 9/5
9
/
5
degrees Fahrenheit, not 5/9
5
/
9
degree Fahrenheit, is equal to a temperature increase of 1 degree Celsius.

The final answer is D.