Fill in the following blanks with suitable words :
Silkworms spin …............. Of silk fibres.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks us to fill in the blank regarding what silkworms spin to produce silk fibers.

2. **Identifying the Key Term**: Silkworms are known for spinning a specific structure that is essential for silk production.

3. **Connecting to the Life Cycle of Silkworms**: Silkworms undergo a life cycle where they eventually enter a stage where they spin a protective covering around themselves.

4. **Recognizing the Structure**: The structure that silkworms spin is called a "cocoon." This is where they form a shell-like structure made of silk fibers.

5. **Filling in the Blank**: Based on the information gathered, we can fill in the blank with the word "cocoon."

**Final Answer**: Silkworms spin **cocoons** of silk fibers.

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