Which of the following letter cluster will replace the question mark (?) to complete the given series?

PTX, AEI, LPT, ?

WAE

Explanation:

PTX, AEI, LPT, ?

The logic followed here is :

P → (+11) → A → (+11) → L → (+11) → W

T → (+11) → E → (+11) → P → (+11) → A

X → (+11) → I → (+11) → T → (+11) → E 

So, the letter-cluster that replaces the (?) to complete the series is "WAE"