Final answer:
Brazing is a metal-joining technique executed at temperatures above 450°C (842°F), which is the correct answer (option A).
Step-by-step explanation:
Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal. Unlike soldering, brazing is performed at relatively higher temperatures. Specifically, brazing is performed at temperatures above 450°C (842°F). This is far above the boiling point of water (100°C/212°F) but well below the temperatures mentioned as between 200 and 275 Kelvin, which are far too low and not practical for brazing. Therefore, the correct answer is A) above 450°C.