Step 1: Understanding morphemes.
A morpheme is the smallest unit of meaning in a language. Words can consist of one morpheme (free morphemes) or multiple morphemes (free + bound morphemes). The question asks for unique morphemes, meaning repetitions are counted only once.
Step 2: Breaking the sentence into morphemes.
The sentence is:
{How many unique morphemes can be isolated in this sentence?}
We can isolate the following morphemes:
how
many
unique
morpheme + -s
can
be
isolate + -ed
in
this
sentence
Counting each morpheme only once gives:
how, many, unique, morpheme, -s, can, be, isolate, -ed, in, this, sentence
Total unique morphemes = 12
Step 3: Eliminating incorrect options.
Options (B), (C), and (D) either undercount or overcount morphemes by ignoring bound morphemes or duplicating repeated forms.
Step 4: Conclusion.
When both free and bound morphemes are correctly identified and counted uniquely, the correct total is twelve.
Final Answer: (A) Twelve