The room-temperature electrical conductivity of a semiconductor specimen is 2.8 × 10 4 (ω∙m)–1. if the electron concentration is 2.9 × 1022 m–3 and electron and hole mobilities are 0.14 and 0.023 m2/v∙s, respectively, calculate the hole concentration. (a) 1.24 × 1024 m–3 (b) 7.42 × 1024 m–3 (c) 7.60 × 1024 m–3 (d) 7.78 × 1024 m–3