There is a sentence that is missing in the paragraph below. Look at the paragraph and decide where (option $1, 2, 3$, or $4$) the following sentence would best fit.
$\textbf{Sentence}$: Yet each day the flock produced eggs with calcareous shells though they apparently had not ingested any calcium from land which was entirely lacking in limestone.
$\textbf{Paragraph}$: Early in this century a young Breton schoolboy who preparing himself for a scientific career began to notice a strange fact about hens in his father's poultry yard. $\_\_\_\_\_\_ (1) \_\_\_\_$. As they scratched the soil they constantly seemed to be pecking at specks of mica, a siliceous material dotting the ground. $\_\_\_\_\_\_ (2) \_\_\_\_$. No one could explain to Louis Kervran why the chickens selected the mica, or why each time a bird was killed for the family cooking pot no trace of the mica could be found in its gizzard. $\_\_\_\_\_\_ (3) \_\_\_\_$. It took Kervran many years to establish that the chickens were transmuting one element into another. $\_\_\_\_\_\_ (4) \_\_\_\_$.
- Option $3$
- Option $1$
- Option $2$
- Option $4$