The correct answer is (a) Harrod.
The natural growth rate is the rate of economic growth that can be sustained in the long run without causing inflation or unemployment. It is determined by the rate of population growth, the rate of technological progress, and the rate of capital accumulation.
Roy Harrod was an English economist who developed the Harrod-Domar model of economic growth. The model shows that the natural growth rate is equal to the rate of savings divided by the capital-output ratio. The capital-output ratio is the amount of capital that is needed to produce one unit of output.
If the actual growth rate is greater than the natural growth rate, then the economy will experience inflation. If the actual growth rate is less than the natural growth rate, then the economy will experience unemployment.
(b) Lamarck was a French biologist who developed the theory of acquired characteristics. This theory states that organisms can pass on to their offspring characteristics that they have acquired during their lifetime. However, this theory has been disproved by modern genetics.
(c) Nurkse was an Estonian-American economist who developed the theory of balanced growth. This theory states that economic growth can only be achieved if all sectors of the economy grow at the same rate. However, this theory has been criticized for being too simplistic.
(d) Meade was a British economist who won the Nobel Prize in Economics in 1977. He made significant contributions to the fields of international trade, monetary economics, and economic growth. However, he did not develop the concept of the natural growth rate.