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The ss and zz sounds are paired together because they have the same mouth position. Ss is unvoiced, which means you make only air to make the sound, and zz is voiced, you produce sound with the vocal cords. The position: the front top teeth and the bottom teeth line up together an almost touch. Ss, zz, ss, zz. The backs of the teeth are not touching. They are almost touching. The tongue position: the tongue comes up against the back of the bottom teeth and presses very, very lightly.[s]和 [z]的发音很相似，所以我把它们放在一起讲。Ss是清辅音，也就是说它只需气流通过而发声，而zz是浊辅音，这就需要振动声带来发声。发音位置：靠前的上下排牙齿轻轻闭合。Ss，zz，ss，zz。后部的牙齿并没有靠在一起。它们只是处于几乎闭合的状态。舌头位置：舌头轻轻地抵在下排牙齿。

Word pairs:

sip 啜饮—zip 拉链

dress 裙子—says 说（第三人称单数）

Mississippi 密西西比河—Missouri 密苏里