题目

  Charlie studied in a famous college for four years． He studied hard and did well in all his subjects． He hoped to become a good teacher． This year he left the college and began to work in a middle school． He likes his students and is strict（严格的） with them． He does his best to make his classes lively and interesting．   One day he carefully explained a chemical reaction（反应） to the students of Grade 2 in the chemistry lab．   “Be careful， everyone，” he said loudly． “Before I make the experiment，there're twenty five atoms of carbon（碳原子）13．复数i（1-i）的虚部为（　　）A．iB．1C．-iD．-1