In the sentence given below, four words are tested which may be misspelt or inappropriate in their usage. Select the erroneous word as your answer, or choose 'No error' if all words are correct.

The primary objective of the survey was to gather relevant knowlege about rural employment patterns.

The correct answer is knowlege.

Step-by-Step Explanation:

1. Analyze the Sentence:
"The primary objective of the survey was to gather relevant knowlege about rural employment patterns."

2. Evaluate the Tested Words:
- primary: Spelled correctly. It is used appropriately as an adjective meaning "principal" or "main".
- relevant: Spelled correctly. It is used appropriately as an adjective meaning "pertinent" or "applicable".
- patterns: Spelled correctly. It is used appropriately as a plural noun meaning "regular trends or models".
- knowlege: Misspelled. The correct spelling of the word is knowledge (it includes a 'd' before the 'g').

3. Conclusion:
Since "knowlege" is misspelled in the sentence, it is the erroneous word.