True or False. Justify for full credit.

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(a) If the variance of a data set is zero, then all the observations in this data set are zero.

(b) If P(A) = 0.4 , P(B) = 0.5, and A and B are disjoint, then P(A AND B) = 0.9.

(c) A 95% confidence interval is wider than a 90% confidence interval of the same parameter.

(d) In a right-tailed test, the value of the test statistic is 1.5. If we know the test statistic follows a Students t-distribution with P(T < 1.5) = 0.96, then we fail to reject the null hypothesis at 0.05 level of significance .