Sales of existing U.S. homes fell sharply in January to their lowest level in nine months amid a shortage of properties on the market, an industry group reported Monday in a setback to hopes that housing activity could accelerate this year. The National Association of Realtors (NAR) said home re-sales fell 4.9 percent last month to an annual rate of 4.82 million units, the lowest since April 2014. Tight inventories are hurting sales by limiting the selection of houses available to potential buyers. The lack of supply also is keeping home prices elevated, helping to sideline first-time buyers from the market. Only 4.7 months of supply were listed for sale at the end of December, compared with an average of 5.2 months during 2014, the NAR said. Relatively low mortgage rates and steady job growth have failed to spark more activity from buyers and sellers, raising the possibility of either a spring sales rush or a second consecutive year of weakness in the real-estate market.