Determine the range of pregnancy lengths that cover approximately 99.7% of all pregnancies, given the mean and standard deviation:
Suppose that the lengths of human pregnancies are normally distributed with a mean of 266 days and a standard deviation of 14 days. Complete the following statements.
(a) Approximately $99.7 \%$ of pregnancies have lengths between $\square$ days and $\square$ days.
(b) Approximately ? $\quad$ O of pregnancies have lengths between 238 days and 294 days.
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Step 1 ：Given that the lengths of human pregnancies are normally distributed with a mean of 266 days and a standard deviation of 14 days.

Step 2 ：In a normal distribution, approximately 99.7% of all data falls within 3 standard deviations from the mean.

Step 3 ：Calculate the lower bound of the range by subtracting 3 times the standard deviation from the mean: \(266 - 3 \times 14 = 224\).

Step 4 ：Calculate the upper bound of the range by adding 3 times the standard deviation to the mean: \(266 + 3 \times 14 = 308\).

Step 5 ：Final Answer: Approximately 99.7% of pregnancies have lengths between \(\boxed{224}\) days and \(\boxed{308}\) days.