Which growing condition is least favorable for tilling the fields?

The least favorable growing condition for tilling the fields is indeed cold temperatures with frozen ground. Tilling involves turning over the soil to improve aeration, weed control, and prepare seedbeds. When the ground is frozen, the soil becomes hard and compact, making it nearly impossible to work with.

Frozen ground often leads to damage to the equipment used for tilling because the soil doesn't yield as appropriately as unfrozen soil would. Moreover, the benefits of tilling—such as soil aeration and improved drainage—cannot be achieved when the soil is in a solidified state.

In contrast, the other conditions listed facilitate better tilling. Warm weather with dry soil and hot dry weather with sandy soil allow for easier manipulation of the ground, as both tend to be more workable than frozen soil. Moderate humidity with soft soil provides an ideal environment for tilling due to the moisture content allowing the soil to be easily disturbed without becoming mud-like.