A study of elementary school students, ages 6 to 12, finds a high positive correlation between shoe size x and score y on a test of reading computation. The observed correlation is most likely due to

Select one:

a.a mistake, since the correlation must be zero.

b.cause and effect (larger shoe size causes higher reading comprehension).

c.a mistake, since the correlation must be negative.

d.the effect of a lurking variable, such as age.