When should distress flares and rockets be used （).

It can be inferred from the passage that lichens use less energy and grow more slowly when

When used with reversing reduction gears, medium－speed diesel engines should be bolted to

Trees should only be pruned （修剪, 整枝) when there is a good and clear reason for doing s

The author believes that __________ .A.library resources should be used frequently and com

Trees should only be pruned (修剪 整枝) when there is a good and clear reason for doing s

When he was a boy he used to go there and watch _____.A.to repair bicyclesB.bicycles to be repaired