他们的家族有双胞胎生育的遗传倾向。

There's a genetic tendency for ___twinning in their family.

我们学校和法国一所学校的结对项目促进了学生交流。

The ___twinning between our school and a French one has enhanced student exchanges.

在显微镜下观察，这些石英晶体显示出明显的双晶现象。

Under the microscope, these quartz crystals exhibit distinct ___twinning.