Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

[Q]: Problem: if an investor puts $ 800 in a savings account that earns 10 percent annual interest compounded semiannually, how much money will be in the account after one year ?
Options: a. $ 878, b. $ 880, c. $ 882, d. $ 884, e. $ 886
[A]: c


[Q]: Problem: what is the tens digit of 6 ^ 10 ?
Options: a. 7, b. 3, c. 5, d. 1, e. 9
[A]: a


[Q]: Problem: a man can swim in still water at 3 km / h, but takes twice as long to swim upstream than downstream. the speed of the stream is ?
Options: a. 1.7, b. 1.4, c. 1.1, d. 1.5, e. 1
[A]:
e