Shifts


 * Examples:**

1. The ocean **contains** rich minerals that **washed down** from rivers and streams.

//Contains// is present tense, referring to a current state; //washed down// is past, but should be present (//wash down//) because the minerals are currently continuing to wash down.
 * Corrected**: The ocean **contains** rich minerals that **wash down** from rivers and streams.

2. About noon the sky **darkened**, a breeze **sprang up**, and a low rumble **announces** the approaching storm.

//Darkened// and //sprang up// are past tense verbs; //announces// is present but should be past (//announced//) to maintain consistency within the time frame.
 * Corrected:** About noon the sky **darkened**, a breeze **sprang up**, and a low rumble **announced** the approaching storm.

3. Yesterday we **had walked** to school but later **rode** the bus home.

//Had walked// is past perfect tense but should be past to maintain consistency within the time frame (yesterday); //rode// is past, referring to an action completed before the current time frame.
 * Corrected:** Yesterday we **walked** to school but later **rode** the bus home.