There is no doubt that we are living in a period of enormous population growth. In the past, it (51) thousands of years for the world's population to double in size. (52) today there are more people having families and fewer deaths from diseases. As(a) (53) , the population doubles in only 35 years. A(n) (54) supply of food is only one of the human needs that must be (55) . Overcrowding has a highly undesirable effect on life. For example, if every available piece of land were used for producing food, it would be very difficult to (56) proper housing for people, as would health care and recreation. (57) these reasons, more governments are helping families to understand the problems of (58) population. They give 'family planning' advice to families that request it. Such families can plan to have the number of children they want, at times when they are best able to care (59) children and give them a good start in life. A research center in the Philippines is producing ‘miracle rice', (60) rice that have been highly successful in Asia and in (61) African countries. The significance of such work was recognized by the awarding of the 1970 Nobel Peace Prize (62) one of the plant breeders of the 'green revolution'. (63) to grow well, the improved seeds need large (64) of fertilizer and water, which are not always (65) . Many fertilizers are made up of petroleum, and higher prices for oil have resulted in smaller supplies of fertilizers. 51.