There are three conditions for a unit to recruit employees: first, rich knowledge; Second, skilled; Third, be hardworking. There are four job seekers who meet at least one of the conditions: A, B, C and D. It is known that: 1. A and B are not all knowledgeable; 2. A and D have the same level of knowledge; 3. C and D have the same degree of hard work; 4. Three of the four are knowledgeable, two are hardworking and one is skilled.
After assessment, the unit found that only one of them met all the conditions and he should be D.