I am trying to figure out transitive or intransitive....

It is related to wheat, oats and barley.

related = intransitive?

The stems measure a foot in diameter.

measures - transitive?

Engineers strengthen concrete with it. Intransitive?

Most of these are wrong.

The transitive verbs are those that are followed by nouns or pronouns that answer "What?" or "Whom?" Those are direct objects.

Hint: Direct objects are never in prepositional phrases.

The first two are correct.

Since concrete answers "what" after "strengthen," it is a direct object, making the verb transitive.

The Size might suprise you.

suprise = transitive

Some reach a height of 120 feet.

reach = transitive

The Japanese also make flutes from these stems.

make - transitive

Right!

They're all correct now. :-)

last two, I think I am getting it...

Zoo keepers harvest bamboo for Pandas

harvest = transitive?

In China people eat the tender shoots as a vegetable.

eat = intransitive?

One of those is correct.

Zoo keepers harvest bamboo for Pandas

harvest = transitive?

In China people eat the tender shoots as a vegetable.

eat = transitive?

Right. Shoots is the direct object of eat.

Thank you so much. I think I get it!