What are the two types of innovation that Christensen suggests have the potential to cause disruption

a$.$

An upgrade in the performance of the the products sold in the market $($High$-$End Foothold$)$

b$.$

An innovation in a new market segment$/$adjacent industry offering different attributes not valued in the established market $($New$-$Market Foothold$)$

c$.$

An innovation with very low performance on attributes valued in the market $($Low$-$End Foothold$)$

d$.$

A radical innovation that offers superior performance to existing customers $($First Mover Foothold$)$