The question is testing the knowledge of synonyms. The correct answer is 'Powerful' because it means having great influence or effect, which is the same as 'influential'. 'Glaring' refers to something that is very obvious, usually in a way that is negative. 'Responsible' means being accountable for something. 'Synthetic' refers to something that is made by combining different things or parts, often in a chemical process. Therefore, the other options do not match the meaning of 'influential'.