Answer:
D. threat; challenge
Explanation:
Anything that causes an organisms stress process to initiate is called a stressor.
Threat is something that can cause us harm or something which we perceive might cause us harm.
A challenge is a threat, if overcome can cause us to grow our personality.
So, a threat is something which we cannot overcome while a challenge is a threat which we perceive can overcome and will be beneficial for us.
