A water board's note reads: 'Piped connections in the district have grown by 3,000 households in each of the last three years. At that rate the 21,000 households still without one will all be connected within seven years.' The note's reasoning is most open to criticism because it

Three thousand a year was achieved on the cheapest work there was, and the work left is the dearest — long mains for few houses. A rate got from the easy part of a task will not hold over the hard part, so the seven years is an estimate of what would happen if the task did not change, and the task has changed. How many are already connected does not affect the rate at all; the accuracy of the record is not in dispute; and household size has nothing to do with how fast connections are laid.