The word "be deterred by" (in paragraph 1) means ().

A. be retaliated by
B. be pred from
C. be couraged by
D. be interested in

Most experts believe that an ever-increasing number of countries and terrorist groups will gain the technical capability to acquire and use chemical and biological weapons. But use of these weapons by hostile states or terrorist groups is not inevitable. Even when locked in bloody conventional wars, nations that have considered using these weapons have generally been deterred by the risk that their opponents would retaliate in the same way or escalate the conflict elsewhere. Terrorist groups with the technical capacity to acquire and use a chemical or biological weapon have typically lacked an interest in doing so, while groups interested in such weapons have generally lacked the necessary technical skills.

Assessing future threats, however, involves more than extrapolation from past trends. In the case of chemical and biological weapons, it appears that the likelihood of use by both hostile states and terrorist groups is growing, and it is clear that even one such at- tack against an unprotected population could be devastating.

Ironically, some experts believe that the technological superiority of the U. S. armed forces is heightening the long-term risks of chemical and biological weapon use by states that wish to challenge the international status quo through aggression. Hostile states that hope to have a fighting chance against a U. S. led military coalition, such as the one that defeated Iraq in 1991, may search for ways to compensate for the inferiority of their own conventional military forces. An obvious answer, and one of grave concern to U. S. military planners, is that such states might turn to an unconventional arsenal, most importantly chemical and biological weapons.

The threat of CBW use by terrorists is of an entirely different character. Terrorists have almost always chosen to kill fewer people than they are able to kill. The main reason is that traditional terrorist strategies seek to draw international attention to a cause without excessively antagonizing public opinion. For a variety of reasons this traditional model of terrorism appears to be changing in ways that make future acts of CBW terrorism more likely. Some terrorist groups appear to be increasingly interested in causing massive casualties, a phenomenon that may stem from a rise in religiously inspired acts of violence, the emergence of new, more fluid terrorist cells, and the perception that traditional, low-casualty terrorist acts have lost the capacity to focus public attention. To date only the Japanese cult Aum Shinrikyo has combined the technical capability with the lethal intent required to carry out an act of CBW terrorism. But national security experts are increasingly concerned that more hostile groups will follow Aum’ s precedent and will do so with greater effectiveness than the cult displayed.