Which of the following statements are true? a. a point estimate of a population parameter θis a single number that can be regarded as a sensible value of θ. b. a point estimate of a population parameter θis obtained by selecting a suitable statistic and computing its value from the given sample data. the selected statistic is called the point estimator of θ. c. the sample mean xis a point estimator of the population mean µ. d. the sample variance 2sis a point estimator of the population variance 2σ. e. all of the above statements are not true if the alternative hypothesis has the form ha then a value less than