When a spacecraft travels, one of the major problems is reentry into the Earth ’s _______.
B
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Theengineersinthislabspentseveralweeks_______theirplansforthenewbicycle.
Ihavenotheardanythingfromhimsincehis_______.
Ifyouhaveanyproblemsduringyourstudyhere,pleasedonot_______tocallmeforhelp
Thisriverformsanatural_______betweenChinaandKorea.
The_______isnearlydead,soIcannotstartthecaragain.