Natural plant extracts contain [F] that show different colours in acids or alkalis. These plant extracts can be used as acid-alkali [G].

The statement seems to be incomplete as it does not provide any specific questions. However, it appears to be discussing the topic of natural indicators.

[F] refers to 'pigments' or 'dyes'. Many plants contain pigments that can change color depending on the pH of the solution they are in. These pigments can act as a pH indicator.

[G] refers to 'indicators'. An indicator is a substance that changes color in response to a chemical change. An acid-base indicator (also known as a pH indicator) is a substance that changes color in response to changes in pH.

So, the completed statement would be: "Natural plant extracts contain pigments that show different colours in acids or alkalis. These plant extracts can be used as acid-alkali indicators."