Some experts believe migrating birds from China's Qinghai Lake nature reserve are spreading the virus;  there others who believe  shipments of poultry and poultry products along with poultry manure are the cause .
Some experts believe migrating birds from China's Qinghai Lake nature reserve are spreading the virus; however, there others who believe it's shipments of poultry and poultry products along with poultry manure .
A
however,
A
it's
D
are the cause