Which of the following is an example of an indirect observation?
a. a scientist counts the exact number of snakes in a field.
b. scientist traps fish and
estimates the population of male and female fish based on the ratios of fish he trapped.
c. a scientist counts every frog in a pond.

b. scientist traps fish and  

estimates the population of male and female fish based on the ratios of fish he trapped.

The key word is estimate. Estimate means that he gives a rough number. There aren't exactly that number of fish.

A. and C. are both exact numbers because the scientists manually count each one. This means these are direct observations, and therefore not the answer.

Hope this helped!

~Just a girl in love with Shawn Mendes

nah.   i'm just sleepy.

there are no contact forces mentioned on the list of choices that you've provided.