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 ap parently 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) ..... .

The correct option is Option 4.

Step-by-Step Explanation:

Let's analyze the flow of the paragraph and the logical placement of the missing sentence:

1. Analyze the Sentence to Insert:
"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."
This sentence highlights a paradox: the chickens produced calcium-rich (calcareous) eggshells despite the complete absence of calcium or limestone in their environment and diet.

2. Examine the Paragraph Locations:
• Location (1): Inserting the sentence here interrupts the introduction of the schoolboy (Louis Kervran) and his observation of the hens pecking at mica.
• Location (2): Placing it here breaks the connection between the chickens pecking at the mica and the question of why they selected the mica (which is discussed in the following sentence).
• Location (3): Placing it here would disrupt the transition from the unsolved mystery of the mica to Kervran's ultimate conclusion about transmutation.
• Location (4): This is the most logical position. The preceding sentence states: "It took Kervran many years to establish that the chickens were transmuting one element into another." The missing sentence explains the exact empirical observation that led to this conclusion (i.e., the chickens producing calcium-rich eggs despite consuming only silica/mica and no calcium). Placing the sentence here provides the necessary context and evidence for Kervran's theory of biological transmutation of elements (from silica/mica to calcium).

Therefore, the sentence fits best at Option 4.