How many independent variables should exist in a well designed experiment

Which would be an adaptation in a rainforest, but not in a tundra? a. ability to store water for a long time b. fur that blends in with snow c. strong claws for killing prey d. a beak that can dig into thick trees

Populations of blue-winged warblers, a type of bird, migrate south in the winter and return to canadian breeding grounds in the spring. as global temperatures have increased due to climate change, spring has started arriving in the warbler's breeding grounds earlier in the year, before the warblers return. warblers now arrive at their breeding grounds too late to select ideal nesting sites and to feed on important early-spring food sources how are populations of blue-winged warblers most likely to be affected by the earlier arrival of spring? o a. populations will go extinct since the warblers will stop migrating to breeding grounds. b. populations will be unaffected since most species can quickly adapt to effects of climate change. c. populations will increase since warmer temperatures are generally beneficial to survival, d. populations will decline since individuals will be less likely to successfully reproduce, reset next

Which of these serves as a reference for comparison during a scientific investigation? a)outcome variable (dependent variable) b) test variable (independent variable) c)control group d)hypothesis