Help me choose the correct null hypothesis PLEASE. The designers of the problem-solving course wish to investigate whether there is a significant improvement in maths scores, at a 5% significance level, subsequent to taking the course. Select the correct null hypothesis, where:

μTC denotes the mean score of those who took the course;
μNC denotes the mean score of those who did not take the course;
μD denotes the difference in means between two related samples.
Di = XTCi - XNCi (and XTCi denotes the score of the ith student who took the course).
Select one:
μTC - μNC = 0
μTC - μNC ≠ 0
μTC - μNC > 0
μTC - μNC 0
μD 0
πTC - πNC 0
σTC - σNC < 0
σTC - σNC ≥ 0
σTC - σNC ≤ 0