User-agent: *
Disallow:
Allow: / 

User-agent: Adsbot-Google
Disallow: /
Allow: landing1.php
Allow: landing2.php
Allow: landing3.php

User-agent: YahooYSMcm*
Disallow: /
Allow: landing1.php 
Allow: landing2.php
Allow: landing3.php

User-agent: MSNPTC*
Disallow: /
Allow: landing1.php
Allow: landing2.php
Allow: landing3.php