Please help me Which meaning of den defines the word as it is used in the sentences?

Carlos was reading an interesting book about a group of pirates who lived long ago. He learned that after raiding other ships, they returned to their den to count their gold and avoid being captured.

A a secret place for having meetings

B a dirty, messy place where people live or gather

C a part of a club for boys

D a hiding place for thieves or robbers

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.