The answer is:
C.a negative symptom.
Schizophrenia is a mental illness that modifies how a person sees and interpretates the world, they often tend to be emotionally dettached from its society and close ones, among the negative symptoms this mental disorders has are Alogia, an inability to talk properly or say coherent things, blunted affect, is an inability to show facial expression or emotions, asociality, the lack of desire to participate in social relations, which all could led to someone just sitting very still all day without saying nothing.
