(Bloomberg) U.S. job openings unexpectedly rose in December, led by increases in business services and retail trade, signaling that companies were looking to add workers as the nation starts getting vaccinated against the coronavirus.The number of available positions increased to 6.65 million during the month from a revised 6.57 million in November, the Labor Department’s Job Openings and Labor Turnover Survey, or JOLTS, showed Tuesday. The median estimate in a Bloomberg survey of economists was for 6.4 million vacancies.The data signal that employers in some industries are looking to add workers, though a rise in Covid-19 infections, a tightening of business restrictions during the month and the slow pace of the vaccine rollout are complicating that effort.The number of people who voluntary left their job increased to 3.29 million, pushing the quits rate to 2.3%. which is the highest since February.Openings that involve workers recalled from layoffs or positions that are only