The Employees of Jones-Day Manufacturing Are Represented by a Union

The employees of Jones-Day Manufacturing are represented by a union.All of the mechanics who repair the company's equipment work day shifts,which means that if equipment breaks down in one of the other shifts,Jones has to pay overtime or suffer lost production.Jones proposes to the union that the mechanics be assigned rotating shifts to solve the problem,but the union refuses.Jones then unilaterally changes the shift assignments in accordance with its proposal.The union,sensing malpractice,goes on strike,and Jones replaces the striking mechanics.Later,the National Labor Relations Board finds that Jones has indeed committed malpractice.If the striking mechanics make an unconditional offer to return to work,Jones:

A) does not have to reinstate the mechanics because they were jurisdictional strikers.
B) does not have to reinstate the mechanics because they were wildcat strikers.
C) must reinstate the mechanics because they were unfair labor practice strikers.
D) must reinstate the mechanics because they were economic strikers.