Answer is From all those aforementioned, the true statement is: Thanh’s grade is 2.5 standard deviations below the mean of the test grades.
explanation
The z scores are standard deviations. If, for example, a tool returns a z score of +2.5, it means that the result is a standard deviation of 2.5. Very high or very low (negative) z scores associated
with very low p values are at the ends of the normal distribution.
