In the Knowledge Production Function $\Delta A _ { t } = \bar { Z } A _ { t } L _ { a t } , \bar { z }$

In the knowledge production function $\Delta A _ { t } = \bar { Z } A _ { t } L _ { a t } , \bar { z }$ represents:

A) natural resources
B) the cost of producing new ideas
C) the marginal cost of labor
D) how good an economy is at generating knowledge
E) labor's wage