I know you edited the question and provided the answer already. But I would like to offer further explanation about it.
Answer:
The phrase that indicates a change in mood within the excerpt is:
d) “interrupted by a shuddering cry”
Explanation:
Mood can be defined as the atmosphere an author creates that involves readers. Usually, word choice and description of the setting, as well as imagery, help produce a certain mood. Readers present an emotional response to the atmosphere - happiness, tranquility, fear etc.
In the excerpt of "Monkey's Paw" we are analyzing here, the initial mood is of incredulity, doubt. The father cannot believe the talisman can actually change his life or grant his wish. That mood persists even as the man sits down at the piano and, most likely absentmindedly, plays some chords. It changes, however, when he utters "a shuddering cry". Readers now know something incredible has happened - and they can predict the talisman worked. The mood is changed from this moment on, no longer conveying doubt, but conveying wonder instead.
