The greatest delta of the world is formed by
Think of it like this. When the question talks about the greatest delta of the world is, your mind should go straight to Ganga and Brahmaputra. In Landforms By River, this is a very common fact. Teachers often repeat it because it comes in exams again and again. Just keep this one line in your head.
Ref: [41st BPSC (Pre) 1996] | NCERT Geography textbooks and Goh Cheng Leong, Certificate Physical and Human Geography, discuss Landforms by River and explain the geographical concepts and processes that support the correct answer for this question.