Explanation:
Prepositions are words used to link nouns, pronouns, or phrases to other words within a sentence. They indicate the relationship between the noun or pronoun and other words in a sentence. In this question, we need to choose the correct preposition to complete the sentence.

The correct answer is option 'B' - increase in productivity.

Breakdown:

Heading: Definition of Preposition

- A preposition is a word that links nouns, pronouns, or phrases to other words within a sentence.
- Prepositions indicate the relationship between the noun or pronoun and other words in the sentence.

Heading: Definition of Increase

- Increase means to make something greater in size, amount, or degree.

Heading: Explanation of the Correct Answer

- In this sentence, we want to show the relationship between increase and productivity.
- We use the preposition 'in' when we want to show an increase in something.
- So, the correct preposition to use in this sentence is 'in'.
- Therefore, the correct answer is option 'B' - increase in productivity.

Heading: Common Prepositions

- Some common prepositions include: in, on, at, to, for, with, from, of, about, by, between, among, etc.

Conclusion:

In conclusion, prepositions are important in linking words within a sentence. In this question, the correct preposition to use is 'in' to show the relationship between increase and productivity. It is essential to understand the correct usage of prepositions to communicate effectively in English.

We want to see big increase (in) productivity.

So, (Option 'B') is the correct answer.