The correct answer is: None of these
The distance between two automatic signals can vary depending on a number of factors, including the type of road, the speed limit, and the traffic volume. In general, however, the distance between two automatic signals is typically between 1 and 2 kilometers.
Option A: 2 km. This is a common distance between two automatic signals, but it is not always the case. For example, in areas with high traffic volume, the distance between two automatic signals may be shorter.
Option B: 1 km. This is a shorter distance than is typically used between two automatic signals. However, it may be used in areas with low traffic volume or where there is a need to reduce the speed limit.
Option C: 3 km. This is a longer distance than is typically used between two automatic signals. However, it may be used in areas with high speed limits or where there is a need to increase the distance between two automatic signals.
Option D: None of these. This is the correct answer because the distance between two automatic signals can vary depending on a number of factors.