3. We are flying from San Francisco to Australia. Looking back the last thing we observe of San Francisco is the Golden Gate Bridge. Choose the answer that best explains why the bridge was the
last bit of San Francisco that we observed.
Since the Earth is a sphere the last thing that was observed was the tallest: the bridge.
50 miles out is as far as is possible to see through air.
as we traveled away from San Francisco the bridge was the last thing we saw because of large
its size.
because of the water vapor in the air everything disappeared in the haze. The bridge was the
largest structure so we saw it last.

Since the Earth is a sphere the last thing that was observed was the tallest: the bridge.

Explanation:

As the Earth is a sphere, we are unable to see too far away because light travels in a straight line so cannot travel around the globe. Our vision is therefore restricted to the point where the straight line and the curve of Earth diverge.

The higher the altitude and structure, the longer the divergence will take to happen. This is why the higher you go, the further you will see and the more you will be visible. The San Francisco bridge was the tallest structure and so was the most visible.  

show options, then i will gladly answer you question.

have a good day.