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The research on otters` environmental requirements is surprisingly (i)_____. One reason for this has to do with the estimation of how much they use different areas. Doing so may be (ii)_____ in some kinds of terrain, such as Shetland where the Eurasian otters are active in daytime and have clear individual markings. There it is possible to identify the individuals over stretches of coast of a few kilometers and to see what kinds of coast they use. However, the field conditions are (iii)_____.
- quite problematic
- relatively simple
- largely unnecessary
difficult , relatively simple , exceptional 显示答案