complete the text with the correct form of the verbs in brackets

If you____ (want) to see the
stars and planets, you _____
(can) make your own telescope. All you need is a cardboard tube - the ones you ____ (use) if you want to send a poster by mail - and a couple of lenses
Make sure you cut the tube very straight.
This is important, as you ____
(not be able to ) change the focus unless it ____( be) absolutely straight
Then attach the lenses inside the tube.
You can just slide them in, but if you ____ (need) to make them
secure, glue them in carefully. Finally, cover the other end of the tube with card and make a small hole in the end to look
through. Now you're ready to look at the stars! It's not the world's most powerful
telescope, but if you ____ (use)
it on a clear night, you get some good views. If I ____
(not have) mine, I wouldn't see so much of the night sky.​