Vivek and Ali:
First, Ali's response is a good paraphrase from the PMBOK. However, it really does not answer the original question.
Quantitative risk assessments cost time, treasure and talent to perform correctly and they are not used in all cases because of this. For project management, they are typically performed only on high-value projects.
Choice 4 is the correct answer. See sections 11.3 and 11.4 of the PMBOK for a complete discussion of the two types of risk assessments.
Harry