Every time he spoke to the scientist, the writer felt guilty because
(i) He wasn’t sure what he wanted to ask.
(ii) He forced the scientist to use his voice synthesiser.
(iii) He was face to face with a legend.
(ii) He forced the scientist to use his voice synthesizer.
The Author felt guilty for forcing Hawking to use the synthesizer. To communicate, Hawking had to press the buttons with his thin, weak fingers.