I sincerely suggest you to go through the book WREN AND MARTIN and make yourself strong in the fundamentals, it is a prerequisite to do well in english section .
Studying WREN AND MARTIN for GMAT is similar to climbing mount Everest for scaling a average height peak...
...no offences please....
But yes, one may go through only the relevant chapters if the need arises
IMO GMAT tests very few sections of grammar for which the mgmat SC
book or Aristotle SC grail is more than sufficient..
Fire the final bullet only when you are constantly hitting the Bull's eye, till then KEEP PRACTICING.
A WAY TO INCREASE FROM QUANT 35-40 TO 47 : a-way-to-increase-from-q35-40-to-q-138750.html
Q 47/48 To Q 50 + the-final-climb-quest-for-q-50-from-q47-129441.html#p1064367
Three good RC strategies three-different-strategies-for-attacking-rc-127287.html