CLOZE COMPREHENSION - II. In the following passage, some words have been deleted. Fill in the blank with the most appropriate option.

Passage: The Nobel Prize for Chemistry this year is a tribute to the power of __(46)__. The laureates harnessed evolution and used it in the __(47)__ with amazing results. Frances H. Arnold, an American who was given one-half of the prize, used 'directed evolution' to __(48)__ variants of naturally occurring enzymes that could be used to __(49)__ biofuels and pharmaceuticals. The other half went to George P. Smith, also of the U.S., and Sir Gregory P. Winter, from the U.K., who evolved antibodies to __(50)__ autoimmune diseases and even metastatic cancer through a process called phage display.

Blank (50): ...who evolved antibodies to __(50)__ autoimmune diseases and even metastatic cancer through a process called phage display.