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41. Many subatomic nuclear particles are ______ and nearly ______ : they are hard to track as well as to detect.
A. unstable, explosive
B. elusive, imperceptible
C. minute, immobile
D. charged, reactive
E. tenuous, indivisible
42. The crafty child tricked his innocent brother, a particularly ______ and trusting boy, into committing a mischievous prank.
A. guileless
B. intrusive
C. astute
D. opportunistic
E. circumspect
