Learning some English abbreviations is a necessity. Even though they are not "official" vocabulary, they are one of the essentials for communicating with Americans.
It is necessary to know some abbreviations.Though informal,it is something essential to learn to be able to communicate with Americans.
It is necessary to learn something about English abbreviation . It is not official , but it is one of the necessaries that we must learn in regular communicating with Americans.
It's necessary to learn some English abbreviation ,even though that 's not official vocabulary,yet that's the one of things we must learn in order to communicate with Americans normally.
Learn some English abbreviation is necessary, though it is not official of the words, but that's normal communication and the American people must be one of the things the learning.
To learn some English abbreviations is necessary, although it is not official words , it's a must to have normal communication with Americans.
P.S. Although 和 but 不能连用。