US businesses sharply cut the number of open jobs in December for the second straight month, an unusual sign of weakness in an otherwise healthy job market. The number of available positions dropped 5.4%, to 6.4 million. That’s a historically solid number that exceeds the number of those who are unemployed. Yet the Labor Department numbers released Tuesday show that the number of job openings has fallen by more than 1 million in the past year, the biggest annual drop since the Great Recession. Most of that decline has occurred in just the past two months. Job openings are now at the their lowest level in two years.