All terpenes have carbon skeletons made up of_______
A.Isoprene unit
B.Vinyl unit
C.alkenes
D.ethylenes unit

Hint: To answer this question we must have the knowledge about Terpenes. The unit contains alternate double bonds. It is the main component of natural rubber.

Complete step by step solution:
Terpene is also an organic compound that is produced from plants and some insects too. They are the major component of rosin. We mainly see terpene in essential oils that are derived by many plants and flowers. As we know essential oils are used as fragrance in perfumes, additives and flavoring in food.
Terpene is basically a hydrocarbon whole carbon skeleton is made up of isoprene units. However isoprene is not included in biosynthesis but as a linkage unit from head to tail to form chains. They can be classified on the basis of the number of isoprene units it has. The prefix will indicate the number of isoprene units. They are classified as:
Hemiterpenes contain only a single isoprene unit. Monoterpenes, it contains 2 isoprene units. Sesquiterpenes contains 3 isoprene units and diterpenes contains 4 isoprene units. Polyterpene consists of many long chains of isoprene. Polyterpene is contained in natural rubber.
Isoprene is a common name for \[2 - {\text{methyl}} - 1,3 - {\text{butadiene}}\]. It is an unsaturated hydrocarbon and is a colourless volatile liquid. It is obtained by the thermal decomposition on natural rubber. It is produced by many plants and animals. The formula for isoprene unit is as follows:
\[{\text{C}}{{\text{H}}_2} = {\text{C}}({\text{C}}{{\text{H}}_3}) - {\text{CH}} = {\text{C}}{{\text{H}}_2}\]
Hence, the correct option is A

Note: Terpenes are also used in other disciplines such as pharmacy, biotechnology and cosmetics. It is also used as an active ingredient in pesticide to remove the insects. Terpenes are gaining popularity among people which will lead to the increasing demand of terpene.