The correct option is D C
Here, 'the stomach' must be changed to simply 'stomach'. We often say that 'I have an upset stomach' or 'I have stomach upset'. Thus, 'stomach upset' is used as an idiomatic phrase here- the stomach is not really upset but rather what we mean to say is that we have indigestion. So, when we use 'the stomach is upset' it is not idiomatic anymore and sounds as if a thing called stomach will be sad and upset, which is not what we mean to say. Also, the use of 'he' later on in the sentence needs a reference- we need to know what exactly 'he' refers to. Here, it seems to refer to 'the stomach' so 'he will be in bed' sounds like the stomach will be in bed which is not possible because a stomach can't be lying on the bed- there, obviously, has to be a person there. Thus, part C of the sentence is grammatically incorrect. Also, 'one', if used in a sentence, should be used throughout.