Past continuous.

FORM

Positive

I/he/she/it ---> was waiting

You/we/they ---> were waiting

Negative  

I/he/she/he/it ---> was not waiting

You/we/they ---> were not waiting

Short

I/he/she/it ---> wasn't waiting

You/we/they ---> weren't waiting

Questions

Was I/he/she/it ---> waiting?

Were You/we/they ---> waiting?

1.-Interrupted Action in the Past

Use the Past Continuous to indicate that a longer action in the past was interrupted. The interruption is usually a shorter action in the Simple Past. Remember this can be a real interruption or just an interruption in time.

Examples:

•I was watching TV when she called.

•When the phone rang, she was writing a letter.

•While we were having the picnic, it started to rain.

2-.Specific Time as an Interruption

In the fist use, described above, the Past Continuous is interrupted by a shorter action in the Simple Past. However, you can also use a specific time as an interruption.

Examples:

•Last night at 6 PM, I was eating dinner.

•At midnight, we were still driving through the desert.

•Yesterday at this time, I was sitting at my desk at work.

IMPORTANT

In the Simple Past, a specific time is used to show when an action began or finished. In the Past Continuous, a specific time only interrupts the action.

Examples:

•Last night at 6 PM, I ate dinner.

I started eating at 6 PM.

•Last night at 6 PM, I was eating dinner.

I started earlier; and at 6 PM, I was in the process of eating dinner.

3.-Parallel Actions

When you use the Past Continuous with two actions in the same sentence, it expresses the idea that both actions were happening at the same time. The actions are parallel.

Examples:

•I was studying while he was making dinner.

•While Cindy was reading, Irla was watching television.

•Were you listening while he was talking?

While vs. When

Clauses are groups of words which have meaning, but are often not complete sentences. Some clauses begin with the word "when" such as "when she called" or "when it bit me." Other clauses begin with "while" such as "while she was sleeping" and "while he was surfing." When you talk about things in the past, "when" is most often followed by the verb tense Simple Past, whereas "while" is usually followed by Past Continuous. "While" expresses the idea of "during that time." Study the examples below. They have similar meanings, but they emphasize different parts of the sentence.

Examples:

•I was studying when she called.

•While I was studying, she called.

Exercises here!

http://www.englishpage.com/verbpage/verbs3.htm

http://www.ego4u.com/en/cram-up/grammar/past-progressive/exercises?03