Clark County’s labor market experienced “another good month” in December, the region’s economist reported Tuesday, adding 3,900 jobs over the year and posting an annualized growth rate of 2.9 percent.All but two employment sectors showed a net gain in jobs in the 12 months ending in December 2013, according to Scott Bailey, regional labor economist for the state Employment Security Department. Trade, transportation and utilities payrolls ballooned by 1,100 jobs, professional and business services fattened with 800 jobs, construction added 700 positions, and leisure and hospitality chipped in 500 jobs.On the negative side, health care shed 100 jobs. Government employment saw no change over the year.The net job growth over the year included a bump up from November to December of 700 jobs, including 400 in retail trade and 200 in professional services.Meanwhile, the county’s preliminary unemployment rate in December clocked in at 7.4 percent, Bailey wrote in his “Southwest Washington Labor Market News” report, released Tuesday. That’s down from 8.3 percent unemployment in December 2012.However, December’s initial jobless rate of 7.4 percent may be revised upward next month, according to Bailey. The revision would take into account those unemployed county residents who previously worked in Oregon.