Before revision:  Problems thus arise, making the scenario-based test (i) lack of severity guarantees, (ii) easy to hack with intelligent driving policies, and (iii)  inefficient in producing safety-critical instances with limited and expensive testing effort.
After revision:  Problems thus arise, making the scenario-based test (i) lack of severity guarantees, (ii) easy to hack with intelligent driving policies, and (iii) is inefficient in producing safety-critical instances with limited and expensive testing effort.