1. Change each verb to the present perfect form.
In recent years, the emphasis on sustainability in Civil Engineering (increase) significantly.
Engineers Without Borders is a not-for-profit organization which (work) in developing countries since 2001.
Few researchers (investigate) the possibility of human-like locomotion in robots.
The Kyoto Protocol (not achieve) the intended results as it has not been ratified by all countries.
Group 1 (complete) the first assignment, but Group 2 (not start) yet.

2. Past simple or present perfect? Click one of the two forms of the verbs in brackets to select the correct tense.

• All samples (failed / have failed) under the first test condition.
Reason
Because we have the results, it is clear that the testing is complete; that is, past and finished.
• Recent studies (showed / have shown) that...
Reason
It is unclear exactly when the studies were carried out.
• Research conducted in the 1990s (showed / has shown) that...
Reason
The 1990s are past and finished.
• The studies (were not completed / have not been completed) yet.
Reason
The word 'yet' shows that the timeframe for the studies is not past.

• Two years ago, researchers (demonstrated / have demonstrated) the link between...
Reason
'Two years ago' is past and finished.
• Over the past six years, there (were / have been) several exciting developments in the field of mechatronics.
Reason
The exact times of the developments are not specified.
• Lewis's (2004) investigation (proved / has proved) the effect of...
Reason
The exact year is given.
• An investigation (was carried out / has been carried out) recently into...
Reason
'Recently' is the hint.