Constipation Is a Side Effect of Opioid Use Caused by The

Constipation is a side effect of opioid use caused by the:

A) spasmogenic activity of opioids on smooth muscle and mu₂ receptors in the gastrointestinal (GI) tract.
B) spasmolytic activity on smooth muscle and mu₂ receptors in the GI tract.
C) spasmogenic activity on smooth muscle and mu₁ receptors in the GI tract.
D) spasmolytic activity on smooth muscle and mu₁ receptors in the GI tract.