By Colleen Howe and Muyu Xu BEIJING (Reuters) -Oil prices fell on Wednesday as lacklustre economic activity in China, the world’s biggest crude importer, weighed on sentiment, but prices were set for their first monthly gain since September as broadening Middle East conflicts raised supply concerns. Brent crude futures for March, which expire today, fell 31 cents, or 0.4%, to $82.56 a barrel by 0700 GMT. The more actively-traded April contract fell 29 cents to $82.21. U.S. West Texas Intermediate crude futures declined 25 cents, or 0.3%, to $77.57 a barrel. Manufacturing activity in China, the…