1.   Anarchists say their most stubborn problem is poor public relations.

2.   A linchpin in the humanitarian effort, Kabul Airport, remained closed Monday as UN officials dealt with a stubborn problem.

3.   Involuntary bumping, which occurs when planes are overbooked and some passengers are put on later flights, has been a stubborn statistical problem for Delta for two years.

4.   Is it really easier to assume that a stubborn problem cannot be solved than to put time and energy into finding a solution?

5.   Thailand is generally regarded as a US ally in the fight against drugs, particularly heroin, but neighboring countries have posed a stubborn problem for US authorities.

6.   Corzine, the former chairman of Goldman Sachs, pitched himself as a new face who would apply private-sector can-do enthusiasm to stubborn national problems.