Question

what is the one thing u cant do without

Answer 1

we can't see things without eyes.
we can't write without hands.

Answer 2

We cannot live without five important things--Air,water,food,clothing and shelter.They are necessary for survival and we can't do without them.Water is necessary as we cannot be thirsty all the time.Air is necessary for breathing.Food is necessary so as to get energy to survive.Clothing is necessary to protect us from various climatic conditions like low temperature.Similarly, Shelter is required for us to stay in otherwise we would die of those disasters.All these things are very important in our life indeed. We have been evolved so that these are our basic necessities.If we do not get any one of them, we will die.So, these are things we cannot do without.