Translate the following passage into Chinese. Psychologically there are two dangers to be guarded against in old age. One of these is undue absorption in the past. It does not do to live in memories, in regrets for the good old days, or in sadness about friends who are dead. One’s thought must be directed to the future, and to things about which there is something to be done. This is not always easy; one’s own past is a gradually increasing weight. It is easy to think to oneself that one’s emotions used to be more vivid than they are, and one’s mind more keen. … The other thing to be avoided is clinging to youth in the hope of sucking vigour from its vitality. ⋯Animals become indifferent to their young as soon as their young can look after themselves, but human beings, owing to the length of infancy, find this difficult.
       从心理方面来说，到了老年，有两种危险倾向需要注意防止。一是过分地怀念过去。老想着过去，总觉得过去怎么好怎么好，或者总是为已故的朋友忧伤，这是不妥的。一个人应当考虑未来，考虑一些可以有作为的事情。要做到这一点并非总是很容易的；自己过去的经历就是一个越来越沉重的包袱。人们往往会对自己说，我过去感情多么丰富，思想多么敏锐，现在不行了。
       另一件需要避免的事就是老想和年轻人呆在一起，希望从青年的活力中汲取力量。......动物，一旦它们的后代能够自己照料自己，它们就不管了；但是人，由于抚养子女的时间长，是难以这样做的。 
