1.   But today, officials at the weapons laboratory say the category has long been troublesome, given its ambiguous nature.

2.   Even the names given to some tumors hint at their ambiguous nature.

3.   When politicians wax rhetorical about race, they do not allude to the ambiguous nature of the problem, sticking instead to unsupported absolutes.

4.   But it is the ambiguous nature of this conflict that convictions are not yet set in stone.