flash语法错误

if (Number(n)<20) {
n = Number(n)+1;
nn = "a" add n;
duplicateMovieClip("bg1", nn, n*3);
setProperty(nn, _rotation, random(360));
bb = "b" add n;
duplicateMovieClip("bg2", bb, Number(n*3)+1);
setProperty(bb, _rotation, random(360));
cc = "c" add n;
duplicateMovieClip("bg3", cc, Number(n*3)+2);
setProperty(cc, _rotation, random(360));
} else {
}

**错误** 场景=场景 1, 图层=Layer 1, 帧=2:第 3 行: 语法错误。
nn = "a" add n;

**错误** 场景=场景 1, 图层=Layer 1, 帧=2:第 6 行: 语法错误。
bb = "b" add n;

**错误** 场景=场景 1, 图层=Layer 1, 帧=2:第 9 行: 语法错误。
cc = "c" add n;

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