choice C : A new phenomenon visible at Managua’s major intersections is waves of vendors and beggars, many of them children, who mob cars at the stoplights.
的结构是 a new phenomenon +形容词短语做定语+ is waves of verdors and beggars,同位语修饰beggars, + who引导的非限制性定语从句修饰 children.
2。如果结构是“ a new phenomenon +形容词短语做定语+ is waves of verdors and beggars,同位语修饰beggars, + who引导的非限制性定语从句修饰 children”,那么该句即可简化为:A new phenominon is waves of vendors and beggars. (就不是表语从句了)这样一来,“is”怎么不该是"are"?
for example, "A new phenomenon visible at...." emphasizes "Phenomenon"
"A new visible phenomenon" emphasizes "visible phenomenon", which means that there are already some other "visible phenomenons" and this is a new one, which just does not make too much sense...