Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Abstract concept | Concrete example of concept |
| --- | --- |
| measurement | a student poured water into a graduated cylinder and recorded the number of milliliters |
| prediction | a student predicted that mixing two clear liquids would produce a green liquid |
| explanation | a student explained how certain chemical reactions can cause the color of a liquid to change |
| observation | a student reports that a liquid turned green when mixed with another liquid |
Question:
Which of the following is a form of observation? Select the correct choice to answer the question or fill in the blank.
Choices:
(A) a student explained how certain chemical reactions can cause the color of a liquid to change
(B) a student poured water into a graduated cylinder and recorded the number of milliliters
(C) a student predicted that mixing two clear liquids would produce a green liquid
(D) a student reports that a liquid turned green when mixed with another liquid
Answer:
(D) a student reports that a liquid turned green when mixed with another liquid