And the latter began challenging the former.

The period for candidates to begin challenging one another's petitions has already begun and may end by the time the Government approves the plan.

Lilco began challenging the assessments in court and so far has been winning.

In the 60's and 70's, however, activist groups began challenging the use of some of these names, calling them offensive.

In addition, we, as a society, have to begin challenging the notion that paid work is the most important part of life.

They immediately began challenging the sensibilities of this conservative city, organizing concerts and encouraging student clubs.

Dr. Furberg's team began challenging the drugs' safety and effectiveness in 1995.

Consumer advocates began challenging the group in the 1970's, saying it charged exorbitant rates for insurance.

To continue to challenge viewers, she needs to begin challenging herself.

She soon began challenging the senior records, taking the indoor national record with a jump of 4.24 m in March 2009.