The problem requires decoding a simple substitution cipher to find the code for the phrase 'earned maximum points'.

Analyzing Coded Sentences

We are given the following coded sentences:

• 'they play cricket together' = $mv kb lb iv$
• 'they score maximum points' = $gb lb mb kv$
• 'cricket score earned points' = $mb gv kb kv$
• 'points are earned together' = $kv mv ob gv$

Deducing Word Codes

We can deduce the code for each word by comparing the sentences:

• Comparing sentence 1 and 2, the common word is 'they'. The common code is 'lb'. Therefore, they = lb.
• Comparing sentence 1 and 3, the common word is 'cricket'. The common code is 'kb'. Therefore, cricket = kb.
• Comparing sentence 1 and 4, the common word is 'together'. The common code is 'mv'. Therefore, together = mv.
• Comparing sentence 2 and 3, the common word is 'score'. The common code is 'mb'. Therefore, score = mb.
• Comparing sentences 2, 3, and 4, the common word is 'points'. The common code is 'kv'. Therefore, points = kv.
• In sentence 2 ('they score maximum points' = $gb lb mb kv$), we know 'they' = 'lb', 'score' = 'mb', and 'points' = 'kv'. The remaining code 'gb' must correspond to 'maximum'. Therefore, maximum = gb.
• Comparing sentence 3 and 4, the common word is 'earned'. The common code is 'gv'. Therefore, earned = gv.

Finding the Code for 'earned maximum points'

Using the deduced codes:

• earned = $gv$
• maximum = $gb$
• points = $kv$

Combining these codes in order, the code for 'earned maximum points' is $gv gb kv$.

This corresponds to Option A.