Final answer:
To dry concrete in the event of a temperature drop, using a heater, covering with plastic, or applying a curing compound are the effective methods to ensure proper curing and to protect the concrete from cold weather conditions.
Step-by-step explanation:
When faced with a scenario where there is a sudden drop in temperature during the curing process of concrete, it's important to take appropriate steps to ensure that the concrete dries and cures effectively. In the list of provided options, using a heater (Option c) is an effective method to prevent concrete from being affected negatively by cold weather. Covering the concrete with plastic (Option a) can also help maintain the right curing temperature and moisture. Applying a curing compound (Option d) can also be beneficial to help seal in moisture for proper curing. Increasing water content (Option b) is not a recommended approach as it can weaken the concrete mix and does not address temperature issues. Therefore, the best measures to dry concrete if there is a sudden drop in temperature are to use a heater, cover with plastic, and/or apply a curing compound.