Marriage therapists teach a skill called active listening. Each partner takes a turn listening then interprets what he/she has heard and validates(证实)it. There is, however, a problem. It rarely works. For 80 percent of couples, active listening is too hard. Even happy couples have screaming matches. Every time you raise a hot-button issue, such as — the in-laws or money, does your husband suddenly clam up？ More than 80 percent of the time, it is the wife who brings up tricky marital issues, while the husband tries to avoid discussing them. This isn’t a symptom of a troubled marriage — it’s true in most happy marriages. You’ll often hear that staying in a bad marriage is worse, for everybody concerned — especially the children — than getting divorced. That may be true if your home is so full of hostility that it’s like a war zone. But sociologist Linder J. Waite says she has found that 75 percent of couples who rated their marriages as miserable but stayed married were happy five years later. We usually think the strongest marriages are those that survive major traumas, such as bankruptcy or an extramarital affair. But frequently, dealing with the little things, those daily annoyances, eats away at a marriage. "Every couple experiences disappointment as initial romance and passion fade and they discover all their difference," says Wolin. "He doesn’t do enough housework. She is too emotional. He watches too much TV. She’s too lenient(宽容)with the kids. People think of these differences as problems, but they’re actually opportunities to build marital muscles. The phrase "clam up"(Line 5. Para. 1)probably means______.