If xi=total number of nonconformities in a sample of ni inspection units, and there are N samples of different sample size, and x varies according to a Poisson distribution, what will be the value of center line of the u-chart?

• A. \(\bar{u} = \frac{\sum_{i=1}^N \frac{2x_i}{n_i}}{N}\)
• B. \(\bar{u} = \frac{\sum_{i=1}^N \frac{x_i}{2n_i}}{2N}\)
• C. \(\bar{u} = \frac{\sum_{i=1}^N \frac{x_i}{n_i}}{N}\)
• D. \(\bar{u} = \frac{\sum_{i=1}^N \frac{x_i}{n_i}}{2N}\)