Answer:
C. the labor force participation rate falls
Explanation:
Marginally attached workers are not part of labor force, but if they are included and are unemployed then the labor which is actually participating will fall.
As in the labor participation rate = Working labor or simply employed labor divided by total labor force.
Thus, in this case with marginally attached labor, only denominator will increase in the equation.
Therefore, this will state that the labor force participation will fall as marginally attached is considered as unemployed.