Which of the following advances in food production were attributed to the green revolution of the 1960's and 1970's
a. improved land availability
b. drought-resistant varieties of crop plants
c. improved irrigation systems
d. genetically engineered crops

Great amounts of electromagnetic energy from our sun and other bodies in space travel through space. which is a logical conclusion about these electromagnetic waves? their energy must be very their frequency must be very low these waves can travel without a medium they only travel through a vacuum of space