In a certain code,
'blue pen write' is coded as 'ka tu re'
'red pen draw' is coded as 'mo tu si'
'blue brush draw' is coded as 'ka lo si'
(all the codes are two letter coded only)
What is the code for “blue pen”?

The correct option is ka tu.

To find the code for the phrase "blue pen", we can analyze the given coded sentences and compare them to find common words and their corresponding codes:

1. Compare the first sentence with the second sentence:
- 'blue pen write' is coded as 'ka tu re'
- 'red pen draw' is coded as 'mo tu si'
The common word in both sentences is "pen", and the common code in both representations is "tu". Therefore, the code for "pen" is "tu".

2. Compare the first sentence with the third sentence:
- 'blue pen write' is coded as 'ka tu re'
- 'blue brush draw' is coded as 'ka lo si'
The common word in both sentences is "blue", and the common code in both representations is "ka". Therefore, the code for "blue" is "ka".

3. Combining the results:
Since the code for "blue" is "ka" and the code for "pen" is "tu", the code for the phrase "blue pen" is "ka tu".