NandishSS
Until recently, trade flows were of interest mainly to economic experts and executives of large corporations, but since the past few years, the movement of goods and services across national boundaries have become the subject of intense public attention all over the world.
A. since the past few years, the movement of goods and services across national boundaries have become
B. the movement of goods and services across national boundaries since the past few years became
C. the movement across national boundaries of goods and services over the past few years have become
D. over the past few years, the movement across national boundaries of goods and services are becoming
E. over the past few years, the movement of goods and services across national boundaries has become
over is time preposition which decides the tense of the verb. over+period of time shows a time frame from the past until present.
'over past few years" shows a time frame from a point of time a few years ago to present .
this time frame requires present perfect, which show an action begin in the past and continue until present.
remember
over + a period. over the last year is correct.
since+ a point of time in the past
this morning" can go with simple past or present perfect, depending on the context. if this morning is considered a past because time of speaking is afternoon, simple past is used. but if the morning continues until the time of speaking, the morning show a time frame until present, it requires present perfect.
this morning, I learned gmat (this morning I have learned gmat)
when we see time indicator, think about tense. this is simple. read a few lines in grammar book about time preposition and master this point