교재에 있는 내용은 아닌데, 너무 헷갈려서 샘밖에 생각이 안나서 물어봐요.

이런 비슷한 문제가 게속 나와서요. 답이 (C) 라고 하는데. 

그럼 , in natural environment 가 되는데 너무 이상하게 느껴지거든요. 답이 C 가 맞나요?

Scientists studying the behavior of sound waves have discovered why certain frequencies are more easily absorbed by materials in different environments. Unlike similar frequencies in controlled settings, which exhibit consistent absorption rates due to ______ in natural environments, sound waves encounter various obstacles that alter their paths. Consequently, in natural settings, the absorption rates vary significantly, affecting the clarity and intensity of the sound.

Which choice completes the text so that it conforms to the conventions of Standard English? 

A:  varying frequencies;  B:  varying frequencies since 

C:  varying frequencies,  D:  varying frequencies

이것도 같은 형태 문제예요. 답이 이해가 안됩니다 

His actions, driven by a deep sense of alienation and a desire to protect the innocence of others, lead to ______ in the lives of those he encounters. For instance, his interactions with his sister Phoebe reveal his protective nature, while his encounters with strangers often highlight his internal struggles.

Which choice completes the text so that it conforms to the conventions of Standard English?

A:  unexpected consequences; B:  unexpected consequences however

C:  unexpected consequences, D:  unexpected consequences