Correct the following statement by changing the underlined part of the sentence.
Three spheres of the first layer and three of the second layer enclose a site at the centre in a closest packing arrangement, the site is called `ul("tetrahedral site")`.

Explanation

To correct the statement, we need to analyze the arrangement of spheres in a closest packing structure. The original statement is:

"Three spheres of the first layer and three of the second layer enclose a site at the center in a closest packing arrangement, the site is called `tetrahedral site`."

### Step-by-Step Solution:

1. **Understanding the Arrangement**: In a closest packing arrangement, when we have three spheres in the first layer and three spheres in the second layer, they form a specific geometric arrangement.

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