How to get the invoking target of the GNU make Makefile?

for example, I invoke `make` with the following command line:

```
make a-target

```

How can I get the invoking target "a-target" in the Makefile and assign it to a variable?

Further more, if more than one target is specified on the command line:

```
make target1 target2 ...

```

How do I get all of them?