Multilingual BERT (mBERT), a language model pre-trained on large multilingual corpora, has impressive zero-shot cross-lingual transfer capabilities and performs surprisingly well on zero-shot POS tagging and Named Entity Recognition (NER), as well as on cross-lingual model transfer. At present, the mainstream methods to solve the cross-lingual downstream tasks are always using the last transformer layer's output of mBERT as the representation of linguistic information. In this work, we explore the complementary property of lower layers to the last transformer layer of mBERT. A feature aggregatResearch goal: What is the efficiency-performance trade-off (measured in inference latency vs. F1 score) when using different numbers of intermediate tasks for zero-shot cross-lingual transfer on XTREME tasks like PAWS-X and XNLI?Autonomous synthesis report generated by Assignee Research. Tribunal consensus score: 8.2/10.