I believe the main verb in this sentence is “were”. “to respect”, “to be austere” and “to observe” are “infinitives”; and infinitives are not verbs.
Clearly there are a lot of “logically similar” elements here (three to be precise). So, the intent of the sentence is to convey that the military governors and samurai warriors who ruled Japan were trained to do 3 things:
i) respect simplicity
ii) be austere
iii) observe ritualized code of behavior
Hence, these 3 elements should be structurally similar. Let’s look at A. Suppose we “deconstruct” this as: The military governors and samurai warriors who ruled Japan were trained to X,Y, and Z. Then:
i) X=respect simplicity
ii) Y=be austere
iii) Z=ritualized code of observed behavior
The issue is that the “common portion” of the sentence (outside the XYZ structure) makes sense with X and Y, but does not make sense with Z.
i) … were trained to respect simplicity - Correct
ii) … were trained to be austere - Correct
iii) … were trained to ritualized code of observed behavior - Incorrect
However, with B, everything falls in place. The military governors and samurai warriors who ruled Japan were trained to X,Y, and Z. Then:
i) X= respect simplicity
ii) Y= be austere
iii) Z= observe a ritualized code of behavior
The “common portion” of the sentence (outside the XYZ structure) now makes sense with X, Y and Z:
i) … were trained to respect simplicity - Correct
ii) … were trained to be austere - Correct
iii) … were trained to observe a ritualized code of behavior - Correct
This is the simple technique I have learnt from the book I am currently referring to, and seems to work quite well in these kind of questions.