Which of the following must be true for an estimator of a population parameter to be unbiased?.

Ineed the problem dude

Which of the following is an example of an opposing signal? no examplthates given.   i would say, that traffic lights in a city at major intersections direct the flow of traffic in opposite directions so would be an example.also, stop signs on either side of the same street would be an example. at a train crossing, the light for allowing car traffic in opposite directions or not would be another example.

The angle measures would be 70 and 90