What are the basic gates in MOS logic family?

In MOS logic (most cleanly seen in CMOS, where complementary PMOS pull-up and NMOS pull-down networks realize each gate; earlier NMOS/PMOS-only families instead use a switching network to one supply rail plus a load device), a gate's output is produced by transistors switching toward ground or toward the supply rail — and that switching action itself performs a logical inversion. Because this happens in a single stage without any dedicated separate inverting circuit, exactly the gates whose Boolean logic already is an inversion — NAND and NOR — are the ones MOS realizes directly; that is why they are called the basic (and, since either one alone is functionally complete, "universal") gates of the family.

For this question, only one pairing among the given options matches a gate realized directly in a single transistor stage: putting the input transistors in series in the pull-down network gives NAND, and putting them in parallel gives NOR — no extra components are needed. So the basic gates of the MOS logic family are NAND and NOR.

• AND and OR: these are non-inverting. Realizing them in MOS needs a NAND/NOR stage plus an added inverter, so they are derived gates, not basic ones.

• NAND and OR: this pairs a directly-realized inverting gate with a non-inverting gate that still needs the extra inverter stage; this mixed pairing does not describe what MOS produces natively.

• More than one of the above: applying the transistor-level check individually to each pairing shows only one pairing holds; treating several as valid together does not match the check.

• None of the above: applying the transistor-level check individually to each pairing shows that one of them does hold, so ruling out every pairing does not match the check.

Hence NAND and NOR are the basic gates in the MOS logic family.