Please answer the following question: Given the following passage  "Wood has been an important construction material since humans began building shelters, houses and boats. Nearly all boats were made out of wood until the late 19th century, and wood remains in common use today in boat construction. Elm in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).",  answer the following question. Note that the answer is present within the text.  Question: Wood is often used for building houses, boats and?
A:
shelters