(United States of) America; United States; US; America (land mass); the Americas
anthropologist; ethnologist
main course (of a river); mainstream; main current (e.g. of thought)
mid-stream; middle course; middle class
region; limits; stage; level
millennium; one thousand years; (fig.) long time
(approximate) time; around; suitable time (or condition); time of year; season
foundation; basis; bedrock; substrate (circuit board)
sweet potato (Ipomoea batatas)
such ... as; or some such
nutritional value; food value
crop; crops; (agricultural) produce; farm products
together with; as X, then Y (e.g. as we age we gain wisdom, as wine matures it becomes more valuable, etc.)
gradually; steadily; slowly; little by little; step by step; by degrees
upper stream; upper course; upstream; upper classes
to spread (out); to extend; to stretch; to reach to; to get around; to fill (e.g. a space)
to be conceivable that; to be thinkable that
source (e.g. of a river); headwaters; origin of something continuous (language, culture, etc.)
source (of a river); fountainhead; source; origin; root
historic ruins (remains, relics); archeological site
worldwide; global; international; world-famous; world-class
to protect; to guard; to defend; to keep (i.e. a promise); to abide (by the rules); to observe
cornerstone; main point; requirement; need; necessary; required
fort; fortress; stronghold; fortification
which (of three or more); well; now; c'mon
side (of something, or taking someone's side); part; (watch) case
to build; to construct; to erect; to amass (e.g. fortune); to pile up
to intimidate; to frighten; to scare; to threaten (e.g. peace); to jeopardize; to endanger
to (take out and) show; to demonstrate; to point out (finger, clock hand, needle, etc.); to indicate; to show
to go to ruin; to go under; to fall; to be destroyed; to die out; to become extinct
I'm afraid to say; I'm sorry to say; unfortunately
answer; reply; response; answer; solution; result