Which line from paragraph 4 provides a clue to the meaning of the word constricted? "Amazingly, the benefit of the laughter was similar to that of aerobic exercise
"Laughter apparently causes the endothelium to expand in order to increase blood flow."
"This supports earlier scientific findings, which indicated that mental stress causes blood vessels
to narrow."
"Research has established that mental stress is associated with damage to the endothelium, the
protective barrier lining our blood vessels,