The computer in this classroom is than the computer in the math lab.
a most old b oldest c more old d older

The correct answer is D. Older

Explanation:

In English, to make comparisons it is common to use either the Superlative or the Comparative form. In the case of the Superlative form, this is used when an object stands from its group and is formed by adding "-est" to adjectives or "most" before the adjective in the case of long adjectives. On the other hand, the comparative is used when two objects are being compared and formed by adding (-er) to the adjective or (more) before the adjective in the case of long adjectives.

This implies in the case of the sentence "The computer in this classroom is than the computer in the math lab" that compares one computer to the other the form to be used is the Comparative and bearing in mind the adjective "old" is short the correct form is "older".

the whisper is the answer, hope this : )