Which of the following properties would you look for in vectors?
a. they cannot ensure expression.
b. they are small enough to manipulate in the lab.
c. they survive inside cells.
d. they contain a recognizable genetic marker.

d)

In molecular cloning, a clonng vector is an small DNA molecule used to carry foreign genetic material into a cell, so the DNA sould be capable of self-replication and/or being inside the host cell. The characteristics common to the cloning vector are i) self-replicating inside host cell ii) multiple cloning site, which allows the insertion of DNA pieces, so the increment of the number of copies of target DNA, iii) A gene marker that can be used for indicate the success of foreign DNA introduction.

Consdering the above described, If I am supposed to chose an  unique answer among the options Ichose the d.) recognizable genetic marker is a desirable characteristic.

The option c)... We could wrongly think that it is the right choose if we interpretate that it means that the vector is self-replicated. But survive do not implies that the vector is replicated.  

The option a.) is not necessary in a cloning vector, in contrast many times the expression is desired (for example, for productions of proteins in the host cell).

The option b) is not the correct choosing, it is required an small vector but the reason is facilitate the replication of the DNA molecule rather than the manipulation.