Question

Many living organisms respond to things in the environment called _____.

life
observations
stimuli
obstacles

Answer 1

OBSTACLES are hurdles, or barriers that make the life miserable for a organism to live ,
LIFE is what conprises of there regular activities in which migrating , reproducing , searching forprey and shelter are included ,
OBSERVATIONS are gained through different experiment and last but not the least STIMULI, is that affects the organism's way of living , in short habitat
so i would go with , STIMULI....