Which type of enema is typically used to relieve constipation by instilling and retaining fluid for a short period before expelling?

Rationale: A. Lactulose is usually administered orally to soften stools, not as a short-retention enema. B. A Fleet enema is a hypertonic solution that draws fluid into the colon, is retained briefly, and promotes rapid evacuation of stool to relieve constipation. C. Tap water enemas are hypotonic and typically require immediate expulsion, not short retention. D. Mineral oil enemas are retention enemas, meant to soften stool over a longer period, not for rapid evacuation.