Answer:
laughter may have healing properties
Step-by-step explanation:
"this discovery" as stated in the text is actually referring to "laughter may have healing properties".
From the passage, we discover that it was stated that the doctors reveal that laughter may have healing properties.
Also, the last line of the text revealed that "the discovery" is having a phenomenal influence on health care. It is only laughter that can bring something phenomenal among the other options given.
Something phenomenal is referring to something remarkable. Therefore, laughter is what can make bring a phenomenal influence on health care.