Cellular Respiration/Fermentation Problem Leading to Lack of Energy
Short answer
(A) is a possible answer and is indeed cause for fatigue, as pyruvate is needed for the Krebs cycle to run. The krebs cycle is an essential step in the generation of ATP in aerobic organisms. (B) is incorrect because NADH is never transported into the mitochondria in any organism (it is a nonsense answer). 

Background
NADH is not transported into mitochondria. Instead, its electrons are transported into mitochondria, and I quote from Berg et al. (2002):


  NADH cannot simply pass into mitochondria for oxidation by the respiratory chain, because the inner mitochondrial membrane is impermeable to NADH and NAD+. The solution is that electrons from NADH, rather than NADH itself, are carried across the mitochondrial membrane. One of several means of introducing electrons from NADH into the electron transport chain is the glycerol 3-phosphate shuttle (Figure 18.37).


  


  Electrons from NADH can enter the mitochondrial electron transport chain by being used to reduce dihydroxyacetone phosphate to glycerol 3-phosphate. Glycerol 3-phosphate is reoxidized by electron transfer to an FAD prosthetic group in a membrane-bound glycerol 3-phosphate dehydrogenase. Subsequent electron transfer to Q to form QH2 allows these electrons to enter the electron-transport chain.


Hence, (B) is incorrect.

EDIT: Now why would lactate be formed in (A)? Pyruvate builds up in the cell, as it cannot be transported into the mitochondria. Since lactate dehydrogenase has pyruvate as a substrate, the equilibrium of this reaction will be pushed to the right and lactate will be formed:  


Source: wikipedia page on lactate dehydrogenase

The lack of glucose oxidation takes away the main power supply of aerobic organisms, causing fatigue. Lactate buildup may also induce fatigue.  

Reference
Berg et al. Biochemistry 2002, Freeman, New York