The correct option is Due to the effect of continentality..
Explanation
The annual range of temperature is defined as the difference between the mean temperature of the warmest month and the mean temperature of the coldest month. This range is primarily governed by the differential heating and cooling of land and water bodies.
Detailed Analysis:
- Effect of Continentality (Correct): The North-Eastern part of the Eurasian continent represents a vast landmass located far from the moderating influence of the oceans. Land has a lower specific heat capacity than water, meaning it heats up quickly in summer and cools down rapidly in winter. This absence of maritime influence leads to extreme seasonal contrasts, resulting in the highest annual range of temperature globally (e.g., in the Verkhoyansk region of Siberia).
- Warm Ocean Currents (Incorrect): Ocean currents provide a moderating effect (maritime influence). Warm currents generally raise the temperature of coastal regions in winter, thereby reducing the annual temperature range rather than increasing it.
- High Altitude (Incorrect): While altitude reduces the overall mean temperature due to the normal lapse rate, it is not the primary driver for the extreme seasonal variation observed in this region. The extreme range is a function of the land's distance from the sea.
- Intense Cloud Cover (Incorrect): Cloud cover acts as a blanket; it reflects incoming solar radiation during the day and traps terrestrial radiation at night. This process moderates temperatures and reduces the diurnal and annual ranges. North-Eastern Eurasia typically experiences clear skies in winter, facilitating intense radiational cooling.
Key Takeaway: Continentality (distance from the sea) significantly increases the annual range of temperature, whereas Oceanicity (proximity to the sea) reduces it by moderating thermal extremes.