Concept:The underlined letter in "base" is pronounced as the voiceless consonant sound /s/.
Explanation:"Base" is pronounced /beɪs/, so the underlined letter "s" sounds like /s/.
Option A: "boys" = /bɔɪz/, which ends with /z/, not /s/.
Option B: "clash" = /klaʃ/, which ends with /ʃ/, not /s/.
Option C: "lace" = /leɪs/, which contains the same /s/ sound.
Option D: "lazy" = /ˈleɪzi/, which contains /z/, not /s/.
Answer:C. lace