Based on your reading of the following passage, what do you think is the most challenging aspect of combating terrorist attacks?
the 15 executive branch departments are following their national security strategy (nss) created to strengthen our national security. they are preparing for potential emergencies by investing in strong response teams, training, and materials. while these efforts are important, officials worry that terrorists will find ways around the defined strategies, since terrorists seem particularly good at changing the rules, adapting to current opportunities and recruiting previously unidentified supporters of terror.
intentional germ warfare, such as ebola
terrorists finding ways to avoid detection
nuclear weapon proliferation
attacks on our water systems

terrorists finding ways to avoid detection

Explanation:

This passage is explaining shorty and simply that the terrorists are always finding ways to avoid detection and to perform at least some of their planned activities. The terrorist organizations are constantly in search of new ways as to how to gain supporters and activists, be it some that will be directly included into the organization, or some that have became passively radicalized and start to work on their own for the cause. There are lot of ways of doing so with the modern technology, and that is always going in the advantage of the terrorists, and makes more and new problems for the anti-terrorist units in order to stop them.  

athenian democracy developed around the fifth century bc in the greek city-state (known as a polis) of athens, comprising the city of athens and the surrounding territory of attica, and is often described as the first known democracy in the world. other greek cities set up democracies, most following the athenian model, but none are as well documented as athens'.

it was a political system of direct democracy, in which participating citizens voted directly on legislation and executive bills. participation was not open to all residents: to vote one had to be an adult, male citizen, i.e., not a foreign resident, a submissive or a woman, and the number of these was "probably no more than 30 percent of the total adult population."[1]

the longest-lasting democratic leader was pericles. after his death, athenian democracy was twice briefly interrupted by oligarchic revolutions towards the end of the peloponnesian war. it was modified somewhat after it was restored under eucleides; the most detailed accounts of the system are of this fourth-century modification rather than the periclean system. democracy was suppressed by the macedonians in 322 bc. the athenian institutions were later revived, but how close they were to a real democracy is debatable. solon (594 bc), cleisthenes (508/7 bc), and ephialtes (462 bc) contributed to the development of athenian democracy. cleisthenes broke up the power of the nobility by organizing citizens into ten groups based on where they lived rather than on their wealth.

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male citizens in athens could vote on all the decisions that affected the city and serve on juries. however, democracy was not open to everyone. citizen women and children were not allowed to vote. slaves and foreigners living in athens (known as metics) were banned from participating in government.