I don't know how to correct.
1. Archaeological and geological excavations indicate which a primitive type of corn was used as food in North America at least 7,000 years ago.
2. The surface of Venus is obscured by the planet’s thick clouds yet so is invisible to optical instruments.
3. As the centrally control organ of the body, the brain governs the functioning of the body’s other organs.
4. Lactose, a sugar present in milk, is one of simple sugars used in food preparations for infants.
5. The Mississippi riverboat, which evolved from simpler steamship of the early 1800’s, became the dominant form of passenger transport on the Mississippi River.
1. B
2. C
3. B I think C should be replaced with function
4. C
5. B I think D should be replaced with passenger transportation
Hello MM,

The answer for question (1) seems 'that a'. Any thought?
"Indicate that a ..." seems fine to me. (MM, excuse me for butting in)
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1-- which not which a
2-- and not yet
3-- central not centrally (functioning is OK)
4-- of the simple
5-- steamships not steamship (transport is OK)
 rishonly's reply was promoted to an answer.
 pieanne's reply was promoted to an answer.
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Yes, that answer is better than mine. Mine works grammatically but, well-- I really should read the complete sentences for meaning, shouldn't I?