What problem is the author discussing in this section of the text?
the negative effect climate change has on crops
the decrease in rainfall over the past several years
the problem some areas have with weeds and pests
the longer heat waves caused by climate change

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.

in the 1800s, chinese workers migrated to the united states, first to work in the gold mines, but also to take agricultural jobs, and factory work, especially in the garment industry. chinese immigrants were particularly instrumental in building railroads in the american west, and as chinese laborers grew successful in the united states, a number of them became entrepreneurs in their own right. as the numbers of chinese laborers increased, so did the strength of anti-chinese sentiment among other workers in the american economy. this finally resulted in legislation that aimed to limit future immigration of chinese workers to the united states, and threatened to sour diplomatic relations between the united states and china.

letter a is the answer