Certainly, here are the explanations for the correct answers:

Question 27: B. competitor - In this context, "competitor" refers to other countries or entities that could potentially compete or challenge ASEAN in its goals.

Question 28: D. member - ASEAN aims to establish peace in Southeast Asia and establish friendly relations among its member countries, so "member" fits the context.

Question 29: D. which - The sentence is incomplete, but "which" would likely be the correct choice to continue the sentence's meaning logically. ASEAN aims to maintain peace in Southeast Asia and establish friendly relations, which aligns with its purpose.

Question 30: C. maintain - ASEAN has brought countries together and helped reduce poverty in rural areas, indicating a role of sustaining or keeping these improvements, hence "maintain" fits.

Question 31: C. However - This word would fit well in the sentence structure and convey the idea that despite ASEAN's success, there might still be challenges or obstacles ahead.