The cells involved in innate immunity, whose absence increases the chances of developing malignant tumors, are
a) cytotoxic t cells
b) natural killer cells
c) macrophages
d) b cells

The correct option is B (natural killer cells).

Explanation:

Natural killer cells: They are defined as the type of cytotoxic lymphocyte which are critical to the innate immune system. The NK cells play an important role in to provide rapid response to tumor formation, virus infected cells, and acting after three days of infection.

While cancer cells die, they release some antigens, than these antigens are recognized by the immune system, and later they are presented on the immune cells which are known as antigen presenting cells. So, if these cells are absent than they increase the chances of developing malignant tumors.