Three pendulums all have the same length and start from the same height. the first pendulum is very light and has a mass of 67 g. the second pendulum has a mass of 1.5 kg. the final pendulum has a mass of 3.3 kg. assume that the effects of air drag are negligible. which pendulum attains the highest velocity

All three pendulum will attain same velocity

Explanation:

All three pendulum will attain same velocity irrespective of their mass difference in isolated system (means where air drag are negligible) and at same length

As you know when velocity is calculated we can not take mass into account.  

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.