To find out how "MOCK" is written in the given code language, we need to analyze the codes for "PROP" and "RATE" and identify the pattern or rule that is being followed.

Given:
"PROP" is written as "67"
"RATE" is written as "46"

Observations:
- Both codes have two digits.
- The first digit in each code corresponds to the position of the letter in the English alphabet.
- The second digit in each code is the sum of the positions of the first and last letters in the word.

Analysis:
Let's analyze the code for "PROP" first:
- The letter "P" is the 16th letter in the English alphabet, so the first digit is 1.
- The sum of the positions of the first and last letters in "PROP" is 16 + 16 = 32, which is a two-digit number. Therefore, the second digit is 7.

Now, let's analyze the code for "RATE":
- The letter "R" is the 18th letter in the English alphabet, so the first digit is 1.
- The sum of the positions of the first and last letters in "RATE" is 18 + 5 = 23, which is a two-digit number. Therefore, the second digit is 3.

Pattern:
Based on the analysis of the given codes, we can infer the following pattern:
- The first digit represents the position of the first letter in the word.
- The second digit represents the sum of the positions of the first and last letters in the word.

Applying the pattern to the word "MOCK":
- The letter "M" is the 13th letter in the English alphabet, so the first digit is 1.
- The sum of the positions of the first and last letters in "MOCK" is 13 + 11 = 24, which is a two-digit number. Therefore, the second digit is 4.

Therefore, the code for "MOCK" is "14".
Hence, the correct answer is option D) 44.