An advertiser should group their campaigns by:

• type of product or service
• number of keywords
• maximum cost-per-click (CPC) bids
• number of ad groups per campaign

Correct answer is:

• type of product or service

Explanation: A good rule of thumb for creating an effective campaign structure is to mirror your website’s structure. By creating campaigns and ad groups around a specific theme or product, you can create keyword lists that directly relate to the corresponding ad text, and ads that link directly to that product’s page on your website. You can even add keyword-specific URLs to improve the quality and relevance of your ads in your account.

Read more here: https://support.google.com/adwords/answer/2375470?hl=en