Improper gains refer to benefits that have been obtained as a result of a loss to others without a lawful basis or subsequent loss of legal grounds. According to the above definitions, Which of the following are not undue gains:. ['A accidentally dug a diamond from the ground and sold it for 150,000 yuan.', 'Due to the failure of the cash machine, B took an additional 10,000 yuan and the deposit amount did not decrease.', 'Because of customer negligence, forgetting to find change, he kept 33 yuan change as his own.', 'Ding conceals an envelope containing 20,000 yuan that was picked up by a company found in the restaurant.']