A.steady and predictable moves B. light and soft movements C.a dance on the picnic ground D. a flight on the green grass While orbiting Mars, NASA's Mars Reconnaissance Orbiter took images of the planet's surface. In those pictures, lines, like plant vines, appeared to flow down from slopes on Mars. These lines showed up during the warmer seasons and disappeared in the colder seasons. The discovery of the lines suggests that water exists on Mars. Although Mars has long been known to have ice, researchers are sitting on pins and needles hoping more evidence will reveal itself. Water is an essential building block for life. Therefore, with this information, scientists think that finding life on Mars maybe possible. However, confirming the existence of water may take sometime. Scientists have other missions already planned before they take on finding water on Mars. 37. Read the following sentence from the passage. Although Mars has long been known to have ice, researchers are sitting on pins and needles hoping more evidence will reveal itself. What does the phrase "on pins and needles" mean
