To convert the given distance from kilometers to the SI unit of length, which is meters, we need to use the conversion factor between kilometers and meters.

1. Recall that 1 kilometer is equal to 1000 meters.
2. Given distance: 0.004 kilometers.
3. To convert kilometers to meters, multiply the number by 1000:

\(0.004 \, \text{km} \times 1000 \, \frac{\text{m}}{\text{km}} = 4 \, \text{m}\)

Therefore, the correct conversion of 0.004 kilometers to meters is 4 meters.

Now, let's analyze the options to determine which one correctly represents 0.004 kilometers in SI units:

• \(4 \, \text{m}\): This is the correct conversion, as calculated above.
• \(4000 \, \text{mm}\): Converting meters to millimeters (since 1 m = 1000 mm) would indeed give 4000 mm, supporting the correctness, but the SI base unit is meter, making 4 m more appropriate for direct conversion.
• \(400 \, \text{cm}\): Since 1 m = 100 cm, 4 m would be equivalent to 400 cm; however, this answer does not directly convert from kilometers to meters.
• \(0.4 \, \text{m}\): Incorrect, as demonstrated by our calculation showing that 0.004 km equals 4 m.

Conclusively, the correct option for converting 0.004 kilometers to the SI unit of length is 4 meters.