Blue holes are caves that are (1) underwater / high up in the mountains. They were formed millions of years ago when (2) huge earthquakes happened / the land above them fell in and water entered the space. Blue holes are located on land or in the sea. Many of them are very deep and the water inside the holes is usually very (3) rough / calm. Although exploring blue holes is dangerous, many scientists still risk their lives to dive into them. They think that blue holes can tell us a lot about (4) ancient life forms / how the oceans were formed.

Read the passage. (1) the first skateboard was constructed of old roller-skate wheels attached to a piece of wood. (2) improvements were made to the skateboard in 1959. (3) the year that the first commercially made skateboard appeared. (4) soon after, skateboarding began to grow in popularity. (5) in 1963, skateboard manufacturers formed the first professional skateboarding team. (6) that same year, the first organized skateboard competition took place, in california. which is the most effective way to correct the fragment in sentence 3? attach the fragment to sentence 4. attach the fragment to sentence 2. insert the phrase in the united states to the end of the fragment. insert the verb had before the verb appeared.