素不相识: be strangers to each other; be a complete stranger to...; didn't know ... before; have never met [seen] each other before; not to know each other at all; we are not acquainted with each ot
跟上: keep pace with; catch [keep] up with; keep [be] abreast of [with]: 跟上时代的步伐 keep pace with the times; 跟上科学上的最新发展 keep up with the latest development in science; 跟上形势 keep abreast of the cur
