A

To determine the lubricant film thickness, we can use the formula related to viscous flow between two parallel plates. The film thickness can be calculated using the formula:
\[ h = \frac{F}{\mu A V} \]
Where:
- \( F \) is the weight of the body (100 lb)
- \( \mu \) is the viscosity (0.002089 lb.s/ft^2)
- \( A \) is the surface area (3 ft^2)
- \( V \) is the speed (3.5 ft/s)
Plugging in the values:
\[ h = \frac{100}{0.002089 \times 3 \times 3.5} \]
\[ h = \frac{100}{0.02185815} \approx 4571.63 \text{ ft} \]
The calculated lubricant film thickness indicates the required thickness for effective lubrication. Thus, the final lubricant film thickness is approximately \( 4571.63 \text{ ft} \).
Therefore, based on the calculations, the answer should be selected based on the closest answer available.