The Weight of a USB Flash Drive Is 30 Grams $\neq$

The weight of a USB flash drive is 30 grams and is normally distributed. Periodically,quality control inspectors at Dallas Flash Drives randomly select a sample of 17 USB flash drives. If the mean weight of the USB flash drives is too heavy or too light the machinery is shut down for adjustment; otherwise,the production process continues.The last sample showed a mean and standard deviation of 31.9 and 1.8 grams,respectively.The null hypothesis is ______.

A) n $\neq$ 17
B) n = 17
C) $\mu$ = 30
D) $\mu$ $\neq$ 30
E) m ≥ 34.9