một thanh kim loại chưa bị nhiễm điện được cọ xát và sau đó trở thành vật mang điện tích dương đó là do thanh kim loại đã

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.

not too sure thinking all accelerations are pointed down

blue light is scattered in different directions by the tiny molecules of air. blue is scattered more than other colours because it has a shorter distance to travel which results in smaller waves. this is why we see a blue sky most of the time.