What is the difference between standard deviation and standard error?

Standard deviation is the amount of "deviation", or fluxuation, of a set of data from the average value. For example, if I had a value of 4.0 with a standard deviation of 2, that means all of my data points were between the value of 2 and the value of 6. Standard error, on the other hand, is the difference between the value you received and the expected value of the data set. The lower the error number, the less likely the data you got was due to chance.

What even is an antiderivative?

Opposite of a derivative, an antiderivative is the area under the curve of the graph. For example, the antiderivative of the graph of 2X would be the area under the curve, equaling x^2.

What do I do on the English portion of the ACT when it says choose best answer, but there is more than one answer that makes sense?

The correct answer is most often the shortest answer when you are in that situation. For example, when changing the sentence, "Having studied, my mother is a marine biologist", you would choose the best answer as "My mother is..." rather than "My mother has the occupation of...". Though both answers are right, the ACT believes the most concise answer is the best answer.