The clock struck（敲）eight，but I was still on the bed．I could hear it was blowing strongly．“It must be windy outside，” I thought． I came to the small town a week ago． I sold some clothes to a ten and friends．So I tried to meet the manager and ask him to pay for them．I was out of luck（运气不好）．He went to London and I had to wait for him here．There was no theatre here but a cinema．The films were all too old．I preferred staying in the small hotel to sitting in the cold cinema． Half an hour later，I felt hungry．I had to get up．It was white everywhere and some children were skiing down the hill．On my way to the small restaurant，I saw a boy fall on to a rock （岩石）．I ran to him quickly and carried him to a hospital．Soon his parents came here．Now I knew the boy was just the manager's son．He thanked me very much and gave me the money after we had a dinner．

若对可导函数f(x)，恒有$f\left(x\right)+x{f}^{\text{'}}\left(x\right)>0$，则f(x)（  ）