Final answer:
Short-term sounds have the most significant effect on an infant's heart rate, and duration is considered quantitative continuous data.
Step-by-step explanation:
The answer to the question 'Sounds ___ in duration have the greatest effect on an infant's heart rate' is a) Short, which implies short term and easily changed influences on an infant's heart rate are the most impactful.
Regarding the subject '68. Duration (amount of time) is what type of data?', the correct answer is c. quantitative continuous. This is because duration or the amount of time something takes is a measure that can be infinitely divided into smaller units, such as seconds, minutes, and hours, making it continuous rather than discrete.