Read the text and fill in the gaps with the correct form of verbs as per subject and context.

Microplastic particles (a) —— (accumulate) in riverbed sediments that (b) —— (enter) Bangladeshbthrough India's Ganges river, (c) —— (reveal) a recent study published in Elsevier's Ecotoxicology and Environmental Safety Journal. This study (d) —— (mark) the first in Bangladesh to underscore the serious threat (e) —— (pose) by microplastics in transboundary rivers to the marine ecosystem. It shows the role of rivers in transporting these microplastics into the marine system, (f) —— (create) a potential threat to land, water, and human health. The 330-kilometre journey from the Ganges river basin to the Meghna estuary (g) —— (witness) the deposition of microplastics in shoreline water and deep sediments. According to the World Health Organization (WHO), microplastics are an "emerging" pollutant in the environment which is a serious public health concern. Exposure to microplastic particles has human health implications when they enter the human body through the environment, food, water and air. Moreover, microplastics in water (h) —— (float) or sink based on their concentration, duration and degradation rate of the material. Chemicals associated with microplastics (i) —— (be) also hazardous to aquatic life. The research (j) —— (cover) 10 districts in Bangladesh, collecting a total of 180 water and sediment samples from 30 sampling points (k) —— (stretch) from Chapainawabganj to Chandpur's Meghna estuary. The study (l) —— (reveal) that the highest concentration of microplastics (m) —— (detect) near the Hardinge Bridge in Kushtia, while the lowest was at Premtoli Ghat in Rajshahi. The average microplastic concentrations in upstream and downstream water (n) —— (record) at 24 to 50 particles per litre and 26 to 64 particles per litre, respectively.