Which of the following is the correct statement?
1. The slope of the Isoquants represents the MRTS
2. The MRTS of the inputs x and y = $$\frac{{{\text{M}}{{\text{P}}_{\text{x}}}}}{{{\text{M}}{{\text{P}}_{\text{y}}}}}$$
3. The elasticity of substitution between two inputs x and y is proportionate change in the ratio of two inputs divided by proportionate change in the MRTS
4. If degree of homogeneity is greater than one, the production function is increasing returns to fixed factor