The teachers in a middle school are very caring. Some teachers who often volunteer for blood donation make up lessons for students with learning difficulties free of charge. All teachers who subsidize poor students form difficult pairs with needy families, but all teachers who make up lessons for difficult students for free None of them formed difficult pairs with difficult families. Based on the above premise, Which of the following () must be true. ['Some teachers who sponsored poor students did not volunteer blood donations.', "Some teachers who often volunteer blood don't fund poor students.", 'Some teachers who finance poor students often volunteer blood donations.', 'Some teachers who often volunteer for blood donation help with difficult families.']