In addition to being an exercise on tense, number, and prepositional phrases, this is a challenging exercise in what writing teachers call "invention." Students will need to "invent" the details of identity and extension in time and space. Weak writers often omit these details, and this omission accounts for much of the weakness in their writing, both in terms of details and in terms of main-clause length, a major yardstick of syntactic maturity.
     Note that "identity" and "extension in time or space" are the first two of Hume's three basic logical categories, so this is also an exercise in basic logic.

1. {At the Salvation Army} [Adv. (where) to "had been helping"], a friend {of mine}

[Adj. (identity) to "friend"] had been helping {for several years} [Adv. (when) to "had 

been helping"]. [Past, singular]
 

2. Every evening ^[NuA] {of the year} [Adj. (identity) to "evening"], their father reads 

them (IO) a story (DO) {in their room} [Adv. (where) to "reads"] {before bedtime}

[Adv. (when) to "reads"].  [Present, singular]
 

3. Most cattle {in the north} [Adj. (identity) to "cattle"] will stay {in the barns} [Adv. 

(where) to "will stay"] {during the winter} [Adv. (when) to "will stay"]. [Future, plural]
 

4. A soft wind, {during the night} [Adv. (when) to "whispers"], whispers {through the

trees} [Adv. (where) to "whispers"] {by my bedroom window} [Adj. (identity) to "trees"].

[Present, singular]
 

5. {In the barren room} [Adv. (where) to "lit"] {during the storm} [Adv. (when) to

"lit"], several candles {on the table} [Adj. (identity) to "candles"] lit the shadows

(DO) {of the old man} [Adj. (identity) to "shadows"]. [Past, plural]
 

6. {During the night} [Adv. (when) to "will be rustling"], the leaves {of the maple

trees} [Adj. (identity) to "leaves"] will be rustling {in the moonlight} [Adv. (where)

to "will be rustling"].  [Future, plural]