The correct option is
C makes a face like a bulldog chewing a wasp
As Shreya's brother hates spinach, he is expected to make an expression which indicates his distaste. Option A: The phrase, 'poker face' means 'a blank expression'. 'Make a poker face' means 'have an impassive expression on the face that hides one's true feelings'. Normally, one would not hide his distaste/ feelings at home, especially with someone close (like a mother). Hence, option A is not the correct answer.
Option B: The expression, 'makes a face only a mother could hate' does not communicate any meaning. There is no such expression as given in this option. Hence, this option is incorrect.
Option C: The phrase, 'hot potato' refers to a controversial issue or situation which is awkward to deal with. Eg: 'The introduction of the women's reservation bill became a hot potato in the Parliament'. This phrase is not appropriate to express distaste for something. Hence, option C is incorrect.
Option D: The idiom, 'make a face like a bulldog chewing a wasp' means 'make an ugly, unattractive face'. When someone doesn't like something, one of the ways to express it is to make an ugly face. Hence, this option is correct and completes the conversation meaningfully.