What is the main difference between a groin and a jetty?

a$)$ Groins are perpendicular to the shoreline, while jetties are parallel

b$)$ Groins are built to trap sediment, while jetties are built to protect harbors

c$)$ Groins are submerged structures, while jetties are above the waterline

d$)$ Groins are made of concrete, while jetties are made of rock