Jane won't join us for dinner tonight and _____. [ ]

A. neither won't Tom

B. Tom won't either

C. Tom will too

D. so will Tom

某工厂日产出是1000个单位，总成本是4900元，如果产量减少1个单位，则总成本是4890元，在这个产出的范围以内，成本表现出什么特征？