Stats problem (Please help)?

An ecologist is examining whether the number of fish caught in a large river basin and has changed since a fire burned some of the surrounding forested area and vegetation along the river. Data in the form of fishing reports

was available for a five-year period before the fire. From a random sample of 195 fishing reports before the fire,

the mean catch was 6.3 fish with a standard deviation of 1.6. In a random sample of 143 reports three years

after the fire, the mean catch was 7.1 fish with a standard deviation of 2.1.

Which of the following represents the standard error of the difference in the mean number of fish caught before

and after the fire?

A. 1.6/195 + 2.1/143 (square root of the entire thing, I couldn't put the symbol)

B. 1.6 (squared)/195 + 2.1 (squared)/143

C. 1.6 (squared)/195 (the square root of it) + 2.1 (squared)/ 143 (the square root of it)

D. 1.6 (squared)/195 (The square root of the entire thing) + 2.1 (squared)/143 (the square root of the entire thing)

E. 1.6 (squared) + 2.1 (squared)/195+143