What happens when an advertiser sets a daily budget lower than the recommended amount, using the "Standard" delivery method

What happens when an advertiser sets a daily budget lower than the recommended amount, using the "Standard" delivery method?
  A)  Ads will show when a user searches on the advertisers keywords, but the ads rank will be reduced.
  B)  Ads will show each time a user searches on the advertisers keywords, but only during specified time periods
  C)  Ads will not show every time a user searches on the advertisers keywords
  D)  Ads will never show when a user searches on the advertisers keywords