-- What can trees do _________ us ?
--- They can _________ harmful gases and produce oxygen .
A.helping , take in | B.to help , take in | C.helping , take out | D.to help , take care |
-- What can trees do _________ us ?
--- They can _________ harmful gases and produce oxygen .
A.helping , take in | B.to help , take in | C.helping , take out | D.to help , take care |