1. 每两人(一组)：by the way 顺便说一下 | by twos 每两人(一组) | call for 要求

2. 两个地：by twos and threes 三三两两地 | by twos 两个地 | by type 按类型

3. 每两人：by the way 顺便说一下 | by twos 每两人 | call for 要求

4. 两个两个地,成双地：by twos and threes || 三三两两地,零零星星地 | by twos || 两个两个地,成双地 | by usage || 习惯上

2. by twos的解释