The given data shows the number of mobiles (in thousands) manufactured by companies C-1, C-2, C-3 and C-4 in 2017, 2018 and 2019.

Which company manufactured the highest number of mobiles across all the years?

From the graph,

Number of mobiles manufactured by the company C-1 across all years (in thousands) = 59+65+68 = 192

Number of mobiles manufactured by the company C-2 across all years (in thousands) = 62+67+72 = 201

Number of mobiles manufactured by the company C-3 across all years (in thousands) = 68+71+74 = 213

Number of mobiles manufactured by the company C-4 across all years (in thousands) = 59+62+65 = 186

$$\therefore\ $$Company C-3 manufactured the highest number of mobiles across all the years

Hence, the correct answer is Option C