Explanation:

Let's break down the code:

- 'you can start' = 'sent room dark'

- 'can you read' = 'room sent less'

- 'you are good' = 'tyre room spin'

Analyzing the words:

- "you" appears in all three sentences, and its code appears to be the only word common in all = 'room'

- "can" appears in the first and second sentence.

Comparing:

- 'you can start' = 'sent room dark'

- 'can you read' = 'room sent less'

Both have "can" and "you" in common.

Both have 'sent' and 'room' in common. "room" is associated with "you" (since it also appears in the third phrase which doesn't have 'can'), so "sent" must be for "can".

Options:

1. room (for 'you')

2. sent (for 'can')

3. spin (for 'good')

4. dark (for 'start')

So,

Option 2: sent is correct.