On the old-time farm in America there were chickens and turkeys. There were also cows, pigs, and other livestock. But there were very few machines. Most of the work was done by the entire farm family with the help of a 'hired' man. Sometimes extra labourers were needed in busy seasons. Horses provided 79 percent of the power used, human labor 15 percent, and machines only 6 percent. Today all that has changed. On many modern farms machines now supply 96 percent of the power, human labor 3 percent, and horses 1 percent. Modern farms are enterprising businesses which keep only the livestock that can pay its way. The children go to school by bus every morning, the parents work on the farm or in the house, and hired help is seldom needed. Their work has been replaced by a whole army of farm machines. Farmers in the machine age also use the new fertilizers, new sprays, new feeds, new hybrid seeds, and other helps developed by farm sciences. As a result the farmers are able to produce more food with less labour. This means fewer but larger farms and fewer but more prosperous farmers. In old days, most of the work on a farm was done by______. A．all the farm family B．livestock C．farm machines D．both A and B