A factory claims the production of 150 mm thick sound absorption panels has a standard deviation of 5 mm The client concerns that the process is started to produce panels with thickness somewhat greater than the claimed standard deviation. Giving that chi-square (x2) calculated from 8 samples is 0.153 and significant level at 0.1 is used, which of the following statement is true? Select one: a. Critical region is x2<2.167 or >14.067 b. The claims by the factory is true. c. This is a right-tailed test. d. It is a testing of mean.