It can be inferred from the passage that _________.

The correct option is D The increase in heart rate for a fetus while listening to its mother's voice indicates a preference for that voice.
The best choice is (C). In the concluding paragraph, the author uses the results of the research experiment to observe that the fetuses are able to differentiate between the voices. The statement where the researcher says 'voice recognition may play a role in mother-infant attachment' in addition to the above observation implies that option (C) is the best option. Options (B) and (D) are neither mentioned nor implied in the passage and therefore can be eliminated straight away. Option (A) is incorrect as the research discussed in the passage indicates precisely the opposite of what is mentioned in this option.