Teacher:In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.
Teacher: Now, understand the problem? Solve this instance: Question: How high is the gamma radiation from nuclear fuel? Passage:The nuclear fuel elements were made of refractory ceramic based on beryllium oxide, with enriched uranium dioxide as fuel and small amount of zirconium dioxide for structural stability. The fuel elements were hollow hexagonal tubes about long with distance between the outer parallel planes, with inside diameter of . They were manufactured by high-pressure extruding of the green compact, then sintering almost to its theoretical density. The core consisted of 465,000 individual elements stacked to form 27,000 airflow channels; the design with small unattached elements reduced problems related with thermal stresses. The elements were designed for average operation temperature of ; the autoignition temperature of the reactor base plates was only 150 °C higher. The neutron flux was calculated to be 9×10 neutrons/(cm·s) in the aft and 7×10 neutrons/(cm·s) in the nose. The gamma radiation level was fairly high due to the lack of shielding; radiation hardening for the guidance electronics had to be designed.
 Links: a. Beryllium oxide b. Radiation hardening c. Nuclear fuel d. Radiation hardening
Student:
c