Which tube is acceptable for a blood test that requires heparin and must be free of trace elements?

Which of the following is regarded as a cancerous tumor?

a. Fibrotic b. Benign c. Cystic d. Malignant

Carbon monoxide is a dangerous gas because it binds to the same receptor sites on hemoglobin as ________. 

Fill in the blank(s) with the appropriate word(s).