Los amigos son simpáticos.
Los because you can see amigos has an O and not an A ; also simpáticos has an O and not an A which indicates it is masculine and Los is masculine, Las is not
It would be "Diana prefiere que nosotros tragamos la comida para las vacaciones" because you have to conjugate the verb "tragar" for Nosotros, so you would replace the "-AR" ending with "Amos".
Not only does strength training increase your physical work capacity, it also improves your ability to perform activities of daily living (ADL's). You will be able to work harder and longer with the proper weight training activities. It improves bone density.
