D. According to the text young polar bears ... than adult bears. 1) swim more slowly 2) run more quickly 3) are heavier 4) have more body fat

According to the general understanding of polar bear biology, young polar bears are typically smaller and less developed than adult bears. While they may be agile, 'heavier' and 'more body fat' are relative terms. Without the specific text, it's impossible to definitively choose. However, if the text implies a comparison of physical attributes related to survival and growth, then 'heavier' or 'more body fat' could be plausible depending on the context of 'young' versus 'adult' in the text's narrative. Without the text, any choice is speculative.