In human beings , the hollow ball of cells called a , about b days after fertilisation , burrows into the lining of uterus event called implementation. Blanks a , b respectively are

Options

A. Morula, six
B. Blastula , seven
C. Blastocyst seven
D. Gastrula , seven

Answer

To solve the question, we need to identify the correct terms for the blanks A and B.

### Step-by-Step Solution:

1. **Understanding the Context**: The question refers to a stage in human embryonic development where a hollow ball of cells forms after fertilization and then implants into the uterus.

2. **Identifying Blank A**:
- The hollow ball of cells that forms after the zygote undergoes several rounds of cell division is known as the **blastocyst**.
- Prior to reaching the blastocyst stage, the embryo is referred to as a morula, but the question specifically asks for the hollow ball of cells, which is the blastocyst.

3. **Identifying Blank B**:
- The blastocyst typically forms about **6 to 7 days** after fertilization. This is the time frame in which it travels down the fallopian tube and reaches the uterus to implant.
- Therefore, we can conclude that the answer for B is 7 days.

4. **Final Answer**:
- A = Blastocyst
- B = 7

### Summary:
The hollow ball of cells is called a **blastocyst**, and it implants into the lining of the uterus about **7 days** after fertilization.