The correct answer is: Wheat.
Wheat is the second most important cereal crop in the world, after rice. It is a major source of food for humans and animals, and is also used to make a variety of products, such as bread, pasta, and beer. Wheat is grown in temperate climates around the world, and is particularly important in Asia, Europe, and North America.
Maize is the third most important cereal crop in the world, after rice and wheat. It is a major source of food for humans and animals, and is also used to make a variety of products, such as cornmeal, cornstarch, and ethanol. Maize is grown in tropical and subtropical climates around the world, and is particularly important in North America, South America, and Africa.
Gram is a legume that is a major source of protein for humans and animals. It is also used to make a variety of products, such as flour, dhal, and gram flour. Gram is grown in tropical and subtropical climates around the world, and is particularly important in Asia and Africa.
Potato is a starchy, tuberous crop that is a major source of carbohydrates for humans. It is also used to make a variety of products, such as potato chips, french fries, and potato salad. Potato is grown in temperate climates around the world, and is particularly important in Europe, North America, and South America.
In terms of production, wheat is the most important cereal crop in the world, followed by rice and maize. Gram and potato are not as important as wheat, rice, and maize in terms of production.