Answer
C is more dangerous than B, which in turn is more dangerous than A.
Work Step by Step
Comparing A and B, source B is more dangerous than source A because the gamma rays that source B emits have twice the energy of those from source A. All the sources have the same activity, so A and B emit the same number of gamma rays/second.
Relatively speaking, source B is twice as dangerous as source A.
Now comparing B and C, source C is more dangerous than source B. The gamma rays and the alpha particles have the same energy. The table on page 901 shows that the Relative Biological Effectiveness (RBE) of gamma rays is 1, but is about 20 for alpha particles. The effective dose from source C is about 20 times higher than the effective dose from source B.
Relatively speaking, source C is about 20 times as dangerous as source B.
