阅读下面四篇材料，然后从各题所给的四个选项中选出一个最佳答案。
Its fun playing in the snow．But its even more fun when you have
something big and warm to snuggle(依偎)up t0．For the two polar bear
babies，that big warm thing was their mum．Not only did she give them
a ride on her back but she let them use her as a blanket(毯子)as they sat
down in the snow．
Keren Su．a photographer from Washington，the US，was lucky to take these lovely pictures in a
national park in Canada．“I was there to get photos of the polar bear babies．I believe l discovered
the greatest beauty of nature, ”Mr Su said．
In one photo one bear baby seems to be telling the other to keep quiet because their mum needs
to sleep．The two babies were always snuggling up to their mum．
--This was one of my most enjoyable moments during all of my trips, Mr Su said．Polar bear
mothers protected thei
