It's so difficult to follow the ups and downs of a 2-year-old．One moment he's beaming and friendly; the next he's sullen (愠怒的) and weepy, often for no apparent reason. These mood swings, however, are just part of growing up. They are signs of the emotional changes taking place as your child struggles to take control of actions, impulses, feelings and his body. At this age, your child wants to explore the world and seek adventure. As a result, he'll spend most of his time testing limits, his own, yours and his environment's. Unfortunately, he still lacks many of the skills required for the safe accomplishment of everything he needs to do, and he often will need you to protect him. When he oversteps a limit and is pulled back, he often reacts with anger and frustration, possibly with a temper tantrum (发脾气) or sullen rage. He may even strike back by hitting, biting or kicking. At this age, he doesn't have much control over his emotional impulses, so his anger and frustration tend to erupt suddenly in the form. of crying, hitting or screaming. It's his only way of dealing with the difficult realities of life. He may even act out in ways that unintentionally harm himself or others. It's all part of being 2. It's not uncommon for toddlers to be angels when you're not around, because they don't trust other people enough to test their limits. But with you, your toddler will be willing to try things that may be dangerous or difficult, because he knows you'll rescue him if he gets into trouble. Whatever protest pattern he has developed around the end of his first year will probably persist for some time. For instance, when you're about to leave him with a sitter, he may become angry and throw a tantrum in anticipation of the separation. Or he may whimper, or whine and cling to you. or he could simply become subdued and silent. Whatever his behavior, try not to overreact by scolding or punishing him. The best tactic is to reassure him before you leave that you will be back and, when you return, to praise him for being so patient while you were gone. Take solace in the fact that separations should be much easier by the time he's 3 years old. The 'ups and downs' (Para.1) of a 2 year-old refers to______.