Concept:
Ornamental plants are selected according to their landscape use such as rockery, bedding, edging and cut greens.
Step 1: Match Rockery.
Portulaca is suitable for rockery because it grows well in sunny, dry and rocky places.
\[
A\rightarrow II
\]
Step 2: Match Bedding purpose.
Dahlia is commonly used for bedding purpose.
\[
B\rightarrow III
\]
Step 3: Match Edging.
Coleus is used for edging because of its colourful foliage.
\[
C\rightarrow IV
\]
Step 4: Match Cut greens.
Nemesia is matched with cut greens in the given list.
\[
D\rightarrow I
\]
Therefore:
\[
A-II,\ B-III,\ C-IV,\ D-I
\]
\[
\therefore \text{Correct Answer is (A)}
\]