Read the following context and choose the best option to answer the question.
Context: Ca n't be sure about that , though . One step at a time ... " Andy watched , fascinated , and did n't interrupt again . Castin worked with his laptop battery and the elevator 's wiring , cursing a lot as he went .
Question: What was Castin doing ?
Options: 
A. Working on the wiring .
B. Cursing his friend .
C. Buying a D battery .
D. Taking several steps at a time .


A