Many economists believe that a strong economy is characterized by low unemployment, stable inflation, and that businesses invest heavily in new technologies.

✓ Correct Answer: Option B

The original sentence violates parallelism. The list should maintain a consistent grammatical form. Options A, C, and D break the parallel structure established by 'low unemployment' and 'stable inflation', which are noun phrases. Option B, 'heavy investment by businesses in new technologies,' is also a noun phrase, maintaining parallelism.