these were their most dangerous enemies.

2. We have been excavating layers of ash almost six meters thick, which suggests that they might have kept the fire burning all winter.

3. Yes, indeed, as the botanical analyses have been specifically showing us, all the fields around here used to be part of a large shallow lake.

T: What is the same structure in these sentences?

S: "have/ has been doing..."

T: Yes, in this unit, we will learn "have/has been doing sth." That is the present perfect continuous tense.

Step Ⅲ Explanation

Present Perfect Continuous

[HAS / HAVE] + [BEEN] + [V+ing]

Examples:

I have been waiting here for two hours.

She has only been studying English for two years.

Note: When you are using a verb tense with more than one part such as Present Perfect Continuous (has been studying), adverbs often come between the first part and the second part (has only been studying).

Use 1 Duration from the Past until Now

T: We use the Present Perfect Continuous to show that something started in the past and has continued up until now. "for five minutes", "for two weeks", and "since Tuesday" are all durations which can be used with the Present Perfect Continuous. Look at the following examples.

Show the following.

They have been talking for the last hour.

She has been working at that company for three years.

James has been teaching at the University since June.

Use 2 Recently, Lately

T: You can use the Present Perfect Continuous without a duration such as "for five minutes", "for two weeks", and "since Tuesday". Without the durations, the tense gives a more general meaning of "lately". We often use the words "lately" or "recently" in the sentence to strengthen this meaning. Now read these examples.

Show the following.

Recently, I have been feeling really tired.

She has been watching too much television lately.

Mary has been feeling a little depressed.

Important

T: Remember that the Present Perfect Continuous has the meaning of "lately" or "recently." If the Present Perfect Continuous is used in a question such as "Have you been feeling alright?", it suggests that the person looks sick or unhealthy. A question such as "Have you been smoking?" suggests that you can smell the smoke on the person. Using this tense in a question suggests you can see, smell, hear, or feel the