A 10 m aluminium flagpole is installed at 30°C. After 2 days, the temperature drops to -10° C. How much does the height change of the flagpole (in mm)? (Assume thermal expansion coefficient for aluminium = 23 × 10-6°C-1)

• A. 7.8 mm
• B. 8.8 mm
• C. 9.5 mm
• D. 9.2 mm