Answer: collaborating style.
The complete sentence reads: The colaborating style of handling conflict in a team reflects both a high degree of assertiveness and cooperativeness.
The conflict-handling styles are five: competing style, avoiding style, compromising style, accomodating style and collaborating style.
Each one relays on different balance of assertiveness and cooperativeness.
Competing style reflects assertiveness.
Avoiding style: reflects neither assertiveness nor cooperativeness.
Compomissing style: moderate amount of both assertiveness and cooperativeness.
Accomodating style: higher level of cooperativeness.
Collaborating style: high degree of both assertiveness and cooperativeness.