heteachertoldthemsincelight________(travel)fasterthansound,lightning________(appear)togobeforethunder.
________(fail)severaltimes,theyneedsomeencouragement.
Ihavebeenstudyinghereforfouryears,bynextsummerI________.
Night________(fall),wehurriedhome.
________(catch)intherain,hewaswettotheskin.
Tosucceedinascientificresearchproject________.
