Series of six to nine consecutive histidine residues can bind to immobilized metals such as nickel (ni). the purification of a protein containing six histidines at its c-terminus using a nickel-based resin would be achieved by chromatography.

Donald was arrested for murdering an acquaintance. at the trial, donald takes the stand and testifies that he and the victim knew each other. he admits that they would drink and use drugs together. one night while partying, donald explains in his testimony, an argument got out of hand during a card game. donald explains that the victim accused him of cheating and pulled out a knife on him and started swinging it in the air. donald said that he had no choice but to pull out his gun and shoot the victim. the jury convicted donald of manslaughter. who would argue that donald weighed the potential costs and benefits of shooting the victim and decided to pull the trigger as a result of free will? a. a rational choice theorist b. a critical criminologist c. a conflict theorist d. a positivist