What Is the Difference Between Obtrusiveness and Reactivity

What is the difference between obtrusiveness and reactivity?

A) Obtrusiveness is when participants know they are being assessed and reactivity is when participants' awareness influences their performance
B) Obtrusiveness is when participants' awareness influences their performance, and reactivity is when participants know they are being assessed
C) Obtrusiveness is when the assessment is expensive to the participant, and reactivity is when that expense influences participants' performance
D) Obtrusiveness is when the expense of assessment influences participants' performance, and reactivity is when the assessment is expensive to the participant