If the pattern continues in wich of the following years would the comet be visible again?
A 2017
D 2018
C 2019
D 2020

2019 is the answer. The way to solve this is by taking 1956 and take away 1949 from it. You will get 7. Add 7 to 1956. You will get 1963, which is on the chart. Then add 7 to 1963 and you will get 1970, which is also on the chart. Then from that point on keep adding 7 to the year until you get one of the answers. Hope this helps! :3
Here is the order:
1949-1956-1963-1970-1977-1984-1991-1998-2005-2012-2019