$"$U$.$S$.$ worker productrvity growth slowed in the second quarter and labor costs were far weaker than previously estimated in the first quarter, the Labor Department said on Tuesday.

Assuming labour is a variable input, an increase in labour productivity ceteris paribus, will result in$...$

a$)$ A downward shift in the marginal product curve.

b$)$ A dowrward shift in the margnal cost curve

c$)$ An upward shift in the average cost ourve.

d$)$ A dowrrward shif in the production function.