MMA里的GraphicaGrid的问题 求助。

X轴绘制范围小了之后 GraghicaGrid出来的结果两个图变成了小点 。
程序如下：
a = Show[Plot[y = 120, {x, 0, 1},
PlotRange -> {{-.01, .07}, {50, 250}},
PlotStyle -> Directive[Green, Dashed, Thickness[0.005]],
AxesStyle ->
Directive[Black, Arrowheads[0.035], AbsoluteThickness[2],
FontSize -> 45],
LabelStyle -> {FontFamily -> "Times New Roman", GrayLevel[0]},
PlotLegends ->
Placed[LineLegend[{"c"}, LabelStyle -> {Black, 45}],
Scaled[{0.69, 0.9}]]],
ListLinePlot[Import["C:\\Users\\t\\Desktop\\1.xls"],
PlotRange -> {{-.01, .07}, {50, 250}},
PlotStyle -> Directive[Blue, Thickness[0.005]],
AxesLabel -> {"", ""},
AxesStyle ->
Directive[Black, Arrowheads[0.035], AbsoluteThickness[2],
FontSize -> 45],
PlotLegends ->
Placed[LineLegend[{"z"}, LabelStyle -> {Black, 45}],
Scaled[{0.69, 0.9}]], PlotLabel -> None,
LabelStyle -> {FontFamily -> "Times New Roman", GrayLevel[0]}]];
b = Show[Plot[y = 150, {x, 0, 10},
PlotRange -> {{-.01, .07}, {50, 250}},
PlotStyle -> Directive[Green, Dashed, Thickness[0.005]],
AxesStyle ->
Directive[Black, Arrowheads[0.035], AbsoluteThickness[2],
FontSize -> 45],
LabelStyle -> {FontFamily -> "Times New Roman", GrayLevel[0]},
PlotLegends ->
Placed[LineLegend[{"c"}, LabelStyle -> {Black, 45}],
Scaled[{0.69, 0.9}]]],
ListLinePlot[Import["C:\\Users\\t\\Desktop\\2.xls"],
PlotRange -> {{-.01, .07}, {50, 250}},
PlotStyle -> Directive[Blue, Thickness[0.005]],
AxesLabel -> {"", ""},
AxesStyle ->
Directive[Black, Arrowheads[0.035], AbsoluteThickness[2],
FontSize -> 45],
PlotLegends ->
Placed[LineLegend[{"z"}, LabelStyle -> {Black, 45}],
Scaled[{0.69, 0.9}]], PlotLabel -> None,
LabelStyle -> {FontFamily -> "Times New Roman", GrayLevel[0]}]];
GraphicsGrid[{{a, b}}]
结果是这样的：