是one kilometers 还是one kilometer?要写作文 想说 It's only about 1 kilometer 可是不知道一公里加不加s?

是on one hand,还是on the one hand对? 是one kilometers 还是one kilometer?要写作文 想说 It's only about 1 kilometer 可是不知道一公里加不加s? 是in one's life还是on one's life 是on one hand,on the other hand还是on the one hand,one the other hand还是都可以? 是On one's fiftieth birthday 还是 On one's fifties birthday?求救啊,坐等坐等. sit on my hat 是sit on是词语 还是on one’s hat one-on-the-way是形容词还是名词 one morning 还是 on one morning 独自的短语是on one`s own还是in one`s own 是in one's way home 还是on one's way home 在某人的假日里是on one's holiday还是in one's holiday 在某人的假期里是In one's holiday还是on one's holiday? 在某人心中是on one's mind还是in one's mind 是in one's care 还是on one's care ,在某人的照顾下 是on one's way home还是on one's way to home?这个“on one's way有什么用法 是to be one- on- the- way（怀孕的）还是to have one- on- the- way,为什么 在生日那天是写成on one's birthday 还是可以写成on birthday 到底是on the one hand ...,on the other hand还是on one hand...on the other hand?第一个到底有没有the?