Final answer:
The correct order of the planets Earth, Venus, and Mars in decreasing size is Earth, Venus, Mars.
Step-by-step explanation:
The correct order of the planets Earth, Venus, and Mars in decreasing size is option B) Earth, Venus, Mars. Earth is the largest of the three planets, followed by Venus, and then Mars. In terms of size, Earth has a diameter of about 12,742 kilometers, Venus has a diameter of about 12,104 kilometers, and Mars has a diameter of about 6,779 kilometers.