【推荐1】We usually shake hands and say “How do you do?” when first ____(introduce) to each other.

【推荐2】Experts warn that medical waste from hospitals, if not ________(handle) properly, may lead to spreading diseases. （所给词的适当形式填空）

【推荐3】To any neighboring countries, border issues, unless ________ (handle) properly, will directly affect the relationship between them and even lead to conflicts. (所给词的适当形式填空)