This paper reviews mainly on PBL online teaching model and some online teaching practice to explore the necessity that students are supposed to acquire. The paper first introduces the conception of meta-learning skills which can be highly described as learning skills in the process of students' learning. Then, background and objectives on PBL are given in the main body to bring an initial comprehension of PBL learning. The destination of cultivating students' capacity is to facilitate them to tackle real-life scenarios. In addition, the paper takes the case of University of Hong Kong and Wuhan Polytechnic as examples of online teaching to analyze how to carry out the practice of online teaching based on the teaching mode of Project-Based Learning (PBL), and then demonstrates advantages concerning independent ability, communication and collaboration ability and reflection competences, and then summarize this online PBL teaching mode.

This article presents six case studies of L3 production performed by trilinguals in China, aiming to explore the activation status of L1 and L2 during L3 production. Six Mongolian native college students participated as research subjects, and qualitative and quantitative research methods including a think-aloud writing test and interviews, were adopted to examine which language, Mongolian L1 or Chinese L2, were more readily activated in the process of English L3 production, as well as, what roles L1 and L2 play in the process of L3 production and what factors contribute to the activation of L1 and L2. The findings show that Mongolian L1 and Chinese L2 are activated competitively in the process of English L3 production, but for different learners, they are activated to different levels and play different roles. The recency use of background languages, language proficiency and the medium of instruction are decisive factors in determining the activation levels of Mongolian L1 and Chinese L2 for Mongolian native college students in China. Language proficiency, the type and amount of exposure to L3 and the perceived language distance are the factors that contribute the most to activation of L1 and L2 during L3 production.