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.

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.

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)___.

Evaluation of the options:

Option 1: The sentence starting with "Yet each day..." would not fit here. This part of the paragraph is still introducing Kervran’s initial observations about the hens. The focus is on the strange behavior of the hens in relation to mica, not yet the outcome (calcareous eggs). Inserting this sentence here would seem out of place and disrupt the flow of the paragraph. It would feel disjointed because the paragraph hasn't yet explained the significance of the eggs.

Option 2: The sentence wouldn't fit here either. Here, the paragraph is still describing the hens' behavior of pecking at mica, and inserting the sentence about eggs would shift the focus. The focus here is on what the hens are doing (pecking mica), and the sentence about eggs feels disconnected from this point in the narrative. It doesn’t flow with the idea of their actions related to mica, and thus, it would seem disjointed.

Option 3:  The sentence about the eggs fits perfectly here because it explains a key element of the puzzle: the hens are producing eggs with calcareous shells despite not having an obvious source of calcium. This provides an important piece of information that explains why Kervran was puzzled in the first place. It ties directly to the anomaly he is investigating. It flows naturally with the narrative, as the sentence adds to the mystery that Kervran is trying to solve.

Option 4: It won't fit here as the paragraph has already shifted to Kervran's conclusion about the hens’ behavior. Inserting the sentence about the eggs here would introduce new information too late and disrupt the focus on Kervran's final findings. It would feel out of place in the context of the paragraph’s progression.

Therefore, The sentence fits best in Option 3. It helps to explain Kervran's puzzling observations and contributes to the mystery that he's trying to solve, all while maintaining a smooth narrative flow. The other options either disrupt the flow or introduce new information too soon or too late.