What permits some cancer cells in a tumor to resist treatment while other cancer cells die from the treatment?

Cancer is a diseases that remains one of the main causes of death in human and  different methods have being developed to treat cancer.  Thus, drug resistance leads to the failure of tumor treatment while the expression of ATP-binding casette (ABC) is related to the outcome of chemotherapy in cancer treatment. However, the higher the expression of ABC in a tumor the more resistant cancer cells to chemotherapy. 

b brown mice / white sand dunes

1. a host loses nutrients to a parasite

2. a parasite only benefits when the host is alive (cause if the host dies the parasite dies with it )

3. producers to consumers

4. the tapeworm is a parasite

5. they convert energy from the sun (photosynthesis)

6. sunflower-robin (i think im 80% sure)

7. producer

8. consumer

9. prey

10. fresh water snails ( cause the green algea is the producer and the snails are the primary consumers and the small fish consumer so is the big fish)