Before you ...... (start) the experiment, ...... (not/forget) to turn off the gas and ...... (put) on a pair of glasses to protect your eyes from burns.

When you ...... (light) the cigarette, ...... (watch) the flame of both the match and the cigarette both.

When you ...... (perform) this experiment, ...... (pay) attention to the changes of colour of the substance in question. First, it ...... (turn) blue and then red.

Now, ...... (take) the glass from the fridge, ...... (put) it under the microscope and ...... (observe) the changes in fabric.

Well, then, ...... (insert) yet another drop of water and ...... (wait) for the chemical reaction.

If you ...... (add) too much salt to the mixture, it won't work. So ...... (not/try) to make any unnecessary changes.

First, you ...... (need) to choose the right environment and then ...... (get) a permission from the authorities to conduct the experiment. Then, you ...... (can) move on to the interesting part.

To sum up, ...... (make) sure you have enough flour, salt and spice and ...... (add) them to the mixture one by one. If you ...... (put) everything in at the same time, you will spoilt the dish.

To make such a lovely shelf, ...... (buy) some oak wood. ...... (saw) it in equally long pieces and ...... (put) them together. You ...... (need) a hammer and some nails to make everything work well.

The radio isn't broken. Watch me. ...... (take) a screwdriver and some plastic, ...... (open) the back side of the radio and ...... (change) the broken part.

...... (get) some milk, olive oil, butter and marmelade and ...... (start) mixing the ingredients. Then, you ...... (add) some sugar and a pinch of salt and the thing is ready to be served.

OK, let's have a look, shall we? You ...... (take) the hot iron and ...... (wait) for my signal. Then, you ...... (put) it in the big jar of water. Meanwhile, Henry ...... (perform) the rest of the experiment.