A Document-Level Machine Translation Quality Estimation Model Based on Centering Theory.- SAUNLP'S Submission for CCMT 2021 Quality Estimation Task.- BJTU-Toshiba's Submission to CCMT 2021 QE and APE task.- Low-resource Neural Machine Translation based on Improved Reptile Meta-Learning Method.- Semantic Perception-Oriented Low-resource Neural Machine Translation.- Semantic-aware Deep Neural Attention Network for Machine Translation Detection.- Routing Based Context Selection for Document-Level Neural Machine Translation.- Generating Diverse Back-translations via Constraint Random Decoding.- Machine Translation Evaluation Technical Report for CCMT' 2021.- BJTU's Submission to CCMT 2021 Translation Evaluation Task.